Photoelectric conversion device, ranging apparatus, and information processing system

ABSTRACT

A photoelectric conversion device includes a first photoelectric conversion portion configured to generate electrons; a second photoelectric conversion portion configured to generate holes; a charge-to-voltage conversion portion including an n-type first semiconductor region configured to collect the generated electrons and a p-type second semiconductor region configured to collect the generated holes, the charge-to-voltage conversion portion being configured to convert a charge that is based on the electrons and the holes to a voltage; and a signal generation portion configured to generate a signal corresponding to the voltage, the signal generation portion including an amplification transistor.

BACKGROUND OF THE INVENTION

Field of the Invention

The present technique relates to a photoelectric conversion device.

Description of the Related Art

There is a ranging apparatus (distance sensor) using a time of flight(TOF) method. In the TOF method, a target of distance measurement isirradiated with light emitted by a light source, and the light reflectedby the target is received. On the basis of the relationship between thespeed of light and the time period from the irradiation to the lightreception, the distance to the target is calculated. Here, the lightthat has been emitted by the light source for ranging and reflected bythe target is referred to as signal light. The received light includes,in addition to the signal light, light (ambient light) derived from alight source different from the light source for ranging, such asnatural light or artificial light. To enhance the ranging accuracy, itis effective to separate the ambient light and the signal light fromeach other.

Japanese Patent Laid-Open No. 2005-303268 (US Patent Application No.2007/0103748) discloses a technique of removing a componentcorresponding to ambient light by an apparatus that performs ranging byusing a light detecting element. According to the second embodiment ofthis publication, the light detecting element includes a firstphotosensitive unit which has a suitable structure for picking out holesand a second photosensitive unit which has a suitable structure forpicking out electrons. The holes generated at the first photosensitiveunit are held by a hole holding unit through a gate unit, and theelectrons generated at the second photosensitive unit are held by anelectron holding unit through the gate unit. The holes held by the holeholding unit and the electrons held by the electron holding unit arerecombined by a recombination unit, and the carriers remained after therecombination are picked out as object carriers through an output unit.

Japanese Patent Laid-Open No. 2008-89346 (US Patent Application No.2008/0079833) discloses a technique of removing noise derived frombackground light (ambient light) by selectively conducting a pluralityof charge-storage sections and a plurality of capacitors to extract adifference component of charge stored in the plurality of charge-storagesections.

SUMMARY OF THE INVENTION

A photoelectric conversion device according to the present disclosureincludes a first photoelectric conversion portion configured to generateelectrons; a second photoelectric conversion portion configured togenerate holes; a charge-to-voltage conversion portion including ann-type first semiconductor region configured to collect the electronsand a p-type second semiconductor region configured to collect theholes, the charge-to-voltage conversion portion being configured toconvert a charge that is based on the electrons and the holes to avoltage; and a signal generation portion configured to generate a signalcorresponding to the voltage, the signal generation portion including anamplification transistor.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic diagrams for describing a photoelectricconversion device, a ranging apparatus, and an information processingsystem.

FIG. 2 is a schematic diagram for describing an operation of thephotoelectric conversion device.

FIG. 3 is a schematic diagram for describing a circuit of thephotoelectric conversion device.

FIGS. 4A to 4C are schematic diagrams for describing an operation of thephotoelectric conversion device.

FIGS. 5A to 5D are schematic diagrams for describing a structure of thephotoelectric conversion device.

FIGS. 6A to 6D are schematic diagrams for describing structures of thephotoelectric conversion device.

FIG. 7 is a schematic diagram for describing a circuit of thephotoelectric conversion device.

FIG. 8 is a schematic diagram for describing an operation of thephotoelectric conversion device.

DESCRIPTION OF THE EMBODIMENTS

An embodiment provides a photoelectric conversion device capable ofenhancing the accuracy of signals.

In the technique according to Japanese Patent Laid-Open No. 2005-303268(US Patent Application No. 2007/0103748), sufficient consideration isnot given to movements of electrons and holes in the case of using aphotoelectric conversion unit (photosensitive unit) for holes and aphotoelectric conversion unit (photosensitive unit) for electrons. Thus,there is a possibility that electrons and holes will not efficiently becollected and that the accuracy of signals generated based on theelectrons and holes will decrease. Accordingly, the embodiment providesa photoelectric conversion device capable of enhancing the accuracy ofsignals generated based on the electrons and holes.

A photoelectric conversion device according to a first aspect of theembodiment includes a first photodiode that generates electrons, asecond photodiode that generates holes, an n-type first semiconductorregion that collects the electrons generated by the first photodiode, ap-type second semiconductor region that collects the holes generated bythe second photodiode, a signal generation portion to which the firstsemiconductor region and the second semiconductor region are connectedin common, a first potential supply portion that supplies a firstpotential to an anode of the first photodiode, and a second potentialsupply portion that supplies a second potential to a cathode of thesecond photodiode. The second potential is higher than the firstpotential.

According to the first aspect, there is provided a photoelectricconversion device capable of enhancing the accuracy of signals generatedbased on electrons and holes.

In the technique according to Japanese Patent Laid-Open No. 2008-89346(US Patent Application No. 2008/0079833), switching noise (kCT noise)generated at the time of selectively switching the conduction of theplurality of charge-storage sections and the plurality of capacitorsdegrades the signal-to-noise ratio, as described in paragraphs 0109 and0110. Thus, in this technique, it is difficult to accurately extract adifference component of charge stored in the plurality of charge-storagesections. Accordingly, the embodiment provides a photoelectricconversion device that accurately generates a signal corresponding to adifference in charge between a plurality of photoelectric conversionportions.

A photoelectric conversion device according to a second aspect of theembodiment includes a first photoelectric conversion portion thatgenerates electrons, a second photoelectric conversion portion thatgenerates holes, an n-type first semiconductor region that collects theelectrons generated by the first photoelectric conversion portion, ap-type second semiconductor region that collects the holes generated bythe second photoelectric conversion portion, and a signal generationportion to which the first semiconductor region and the secondsemiconductor region are connected in common. A difference between afirst potential supplied to the first semiconductor region and a secondpotential supplied to the second semiconductor region in a reset periodis less than 0.10 V.

According to the second aspect, there is provided a photoelectricconversion device that accurately generates a signal corresponding to adifference in charge between a plurality of photoelectric conversionportions.

In the technique according to Japanese Patent Laid-Open No. 2005-303268(US Patent Application No. 2007/0103748), sufficient consideration isnot given to the configuration of the recombination unit in a case wherethe hole holding unit and the electron holding unit are separatelyprovided. Accordingly, the embodiment provides a photoelectricconversion device capable of obtaining, with a simple configuration, asignal corresponding to a difference in the amount of signal chargegenerated by a plurality of photoelectric conversion portions.

A photoelectric conversion device according to a third aspect of theembodiment includes a first photoelectric conversion portion thatgenerates electrons, a second photoelectric conversion portion thatgenerates holes, an n-type first semiconductor region that collects theelectrons generated by the first photoelectric conversion portion, ap-type second semiconductor region that collects the holes generated bythe second photoelectric conversion portion, and a signal generationportion to which the first semiconductor region and the secondsemiconductor region are connected in common. The first semiconductorregion and the second semiconductor region are connected to each othervia a conductor.

According to the third aspect, there is provided a photoelectricconversion device capable of obtaining, with a simple configuration, asignal corresponding to a difference in the amount of signal chargegenerated by a plurality of photoelectric conversion portions.

In the technique according to Japanese Patent Laid-Open No. 2005-303268(US Patent Application No. 2007/0103748), a timing control unit controlsan applied voltage and thereby individual gate units can be openedalternatively. However, it is difficult to accurately control theapplied voltage at high speed. In particular, if the time lag of ON/OFFswitching between two gate units is large, the accuracy of signalsgenerated based on electrons and holes may be decreased. Accordingly,the embodiment provides a photoelectric conversion device capable ofenhancing the accuracy of signals generated based on electrons andholes.

A photoelectric conversion device according to a fourth aspect of theembodiment includes a first photoelectric conversion portion thatgenerates electrons, a second photoelectric conversion portion thatgenerates holes, a first transfer portion that transfers the electronsgenerated by the first photoelectric conversion portion to an n-typefirst semiconductor region, and a second transfer portion that transfersthe holes generated by the second photoelectric conversion portion to ap-type second semiconductor region. The first transfer portion and thesecond transfer portion are connected to the same node, the firsttransfer portion is brought into an ON state and the second transferportion is brought into an OFF state in response to supply of a firstpotential to the node, and the first transfer portion is brought into anOFF state and the second transfer portion is brought into an ON state inresponse to supply of a second potential to the node.

According to the fourth aspect, there is provided a photoelectricconversion device capable of enhancing the accuracy of signals generatedbased on electrons and holes.

In the technique according to Japanese Patent Laid-Open No. 2005-303268(US Patent Application No. 2007/0103748), sufficient consideration isnot given to how the photoelectric conversion unit (photosensitive unit)for holes and the photoelectric conversion unit (photosensitive unit)for electrons are arranged. Accordingly, the embodiment provides aphotoelectric conversion device that generates, with a simpleconfiguration, signals based on electrons and holes.

A photoelectric conversion device according to a fifth aspect of theembodiment includes a first photodiode that generates electrons, asecond photodiode that generates holes, an n-type first semiconductorregion that collects the electrons generated by the first photodiode, ap-type second semiconductor region that collects the holes generated bythe second photodiode, and a signal generation portion to which thefirst semiconductor region and the second semiconductor region areconnected in common. A p-type third semiconductor region thatconstitutes an anode of the first photodiode and an n-type fourthsemiconductor region that constitutes a cathode of the second photodiodeare electrically isolated from each other by a p-n junction.

According to the fifth aspect, there is provided a photoelectricconversion device that generates, with a simple configuration, signalsbased on electrons and holes.

Hereinafter, the embodiment will be described in detail with referenceto the attached drawings. In the following description and the attacheddrawings, the same elements are denoted by the same reference numeralsthroughout a plurality of figures. Thus, the same elements will bedescribed with reference to the plurality of figures, and thedescription of the elements denoted by the same reference numerals isappropriately omitted.

With reference to FIG. 1A, a description will be given of aphotoelectric conversion device 11 and an information processing systemSYS including the photoelectric conversion device 11. The informationprocessing system SYS includes a ranging apparatus 1 and may furtherinclude at least any one of an information processing apparatus 2, acontrol apparatus 3, a driving apparatus 4, an image capturing apparatus5, a display apparatus 6, and a communication apparatus 7. In theinformation processing system SYS, the photoelectric conversion device11 is included in the ranging apparatus 1. The image capturing apparatus5 may include a photoelectric conversion device different from thephotoelectric conversion device 11 of the ranging apparatus 1.Alternatively, the photoelectric conversion device 11 may function as aphotoelectric conversion device of the ranging apparatus 1 and aphotoelectric conversion device of the image capturing apparatus 5.Application examples of the information processing system SYS will bedescribed below.

The ranging apparatus 1 includes a light receiving unit 10. The rangingapparatus 1 may include a light emitting unit 20. The light receivingunit 10 includes the photoelectric conversion device 11 and an opticalsystem 12 that controls incident light on the photoelectric conversiondevice 11. The light emitting unit 20 includes a light emitting device21 serving as a light source and an optical system 22 that controlsoutgoing light from the light emitting device 21. As the light emittingdevice 21, a light emitting diode may be used because it is capable ofrepeatedly blinking at high speed. The wavelength of light emitted bythe light emitting device 21 may be infrared for the purpose of reducingcolor mixture with ambient light mainly including visible light.Infrared is hard to be visually identified by a human and thus can becomfortably used. However, the embodiment is not limited to infraredlight. The optical systems 12 and 22 each include a lens, a diaphragm, amechanical shutter, a scattering plate, an optical low-pass filter, awavelength selection filter, and so forth. For example, the opticalsystem 12 may include a filter having a higher transmittance forinfrared light than that for visible light. The ranging apparatus 1illustrated in FIG. 1A includes the optical systems 12 and 22, but atleast any one of these optical systems may be omitted. In the case ofusing laser light as a light source, the optical system 22 may include ascanning optical system for scanning the light emitted by the lightemitting unit 20 toward a predetermined region. The ranging apparatus 1may include a control unit 30 that is connected to at least one of thelight receiving unit 10 and the light emitting unit 20. The control unit30 drives and/or controls at least one of the light receiving unit 10and the light emitting unit 20. The control unit 30 according to theembodiment that is connected to both the light receiving unit 10 and thelight emitting unit 20 is capable of driving and/or controlling both thelight receiving unit 10 and the light emitting unit 20, and specificallyis capable of driving and/or controlling both of them insynchronization. The control unit 30 is also capable of operating inresponse to a signal received from the information processing apparatus2. The ranging apparatus 1 may include a processing unit 40 that isconnected to the light receiving unit 10. The processing unit 40processes signals output from the light receiving unit 10. The signalsprocessed by the processing unit 40 may be transmitted to theinformation processing apparatus 2. At least one of the control unit 30and the processing unit 40 is capable of operating in response to asignal received from the information processing apparatus 2.

Light 81 emitted by the light emitting unit 20 is applied to a target 9,is reflected by the target 9, and is received as signal light 82 by thelight receiving unit 10. A difference based on the distance from theranging apparatus 1 to the target 9 and the speed of light (3×10⁸ m/s)is generated between a light emission time at the light emitting unit 20and a light reception time at the light receiving unit 10. With thephysical amount corresponding to the time difference being detected, thedistance from the ranging apparatus 1 to the target 9 or informationbased on the distance from the ranging apparatus 1 to the target 9 canbe obtained as, for example, image data. The ranging apparatus 1 is aranging apparatus using a time of flight (TOF) method. The degree of theabove-described time difference can be detected by measuring a phasedifference of light that periodically changes or the number of lightpulses. A large interval between the light emitting unit 20 and thelight receiving unit 10 could make a ranging algorithm complicated, andthus the interval between the light emitting unit 20 and the lightreceiving unit 10 may be set to be shorter than the intervalcorresponding to desired ranging accuracy. For example, the intervalbetween the light emitting unit 20 and the light receiving unit 10 isset to 1 m or less.

Not only the signal light 82 but also ambient light 83 derived from alight source other than the light emitted by the light emitting device21 as a light source enter the light receiving unit 10. The light sourceof the ambient light 83 is natural light or artificial light. Theambient light 83 is a noise component when ranging is performed. Thus,if the ratio of the ambient light 83 to received light is high, thedynamic range of a signal based on the signal light 82 decreases or theS/N ratio decreases, and it is difficult to accurately obtain distanceinformation from the signal light 82. The photoelectric conversiondevice 11 according to the embodiment is capable of removing at leastpart of a component resulted from the ambient light 83 from a signalgenerated based on the light received by the photoelectric conversiondevice 11. Accordingly, the ranging accuracy can be enhanced. Althoughthe details will be described below, in the embodiment, at least part ofa component resulted from the ambient light 83 is removed by using asignal corresponding to a difference in the amount of signal chargegenerated by a plurality of photoelectric conversion portions.Furthermore, with use of electrons and holes as signal charge, thedifference in the amount of charge can be accurately detected by using asimple structure. Accordingly, the ranging accuracy can be enhanced.

An overview of the photoelectric conversion device 11 according to theembodiment will be described with reference to FIG. 1B. Thephotoelectric conversion device 11 includes a cell array 110 on asemiconductor substrate 100. The cell array 110 includes a plurality ofphotoelectric conversion cells 111, which are arranged in a matrixformed of a plurality of rows and a plurality of columns. Thephotoelectric conversion device 11 may also include, on thesemiconductor substrate 100, row wiring lines 120, column wiring lines130, a driving part 140, a control part 150, a signal processing part160, a scanning part 170, and an output part 180. The plurality ofphotoelectric conversion cells 111 in the cell array 110 are connectedto the driving part 140 through the row wiring lines 120 located on thesemiconductor substrate 100 in units of rows. The driving part 140selectively inputs drive signals, such as transfer signals or resetsignals, to the plurality of photoelectric conversion cells 111sequentially or simultaneously. The plurality of photoelectricconversion cells 111 in the cell array 110 are connected to the signalprocessing part 160 through the column wiring lines 130 located on thesemiconductor substrate 100 in units of columns. The signal processingpart 160 processes the signals output from the photoelectric conversioncells 111 through the column wiring lines 130. The signal processingpart 160 may include, for each column of the cell array 110, a CDScircuit, an amplification circuit, and an AD conversion circuit. Thescanning part 170 causes the signals that have been output from the cellarray 110 to the signal processing part 160 through the individualcolumn wiring lines 130 and processed by the signal processing part 160and that correspond to the individual columns to be sequentially outputfrom the signal processing part 160 to the output part 180. The outputpart 180 outputs the signals received from the signal processing part160 to the outside of the photoelectric conversion device 11 and mayinclude an amplification circuit, a protection circuit, and an electrodefor establishing a connection with an external circuit. The control part150 generates control signals and controls the operation timings of thedriving part 140, the signal processing part 160, the scanning part 170,and the output part 180 by using the control signals.

An on-chip lens array (microlens array) and a wavelength filter may beprovided on an incidence surface side of the semiconductor substrate100. The incidence surface side may be identical to the side on whichthe row wiring lines 120 and the column wiring lines 130 are provided onthe semiconductor substrate 100 (front surface side). With thisarrangement, a front-surface-irradiation photoelectric conversion devicecan be obtained. If the incidence surface side is opposite to the sideon which the row wiring lines 120 and the column wiring lines 130 areprovided on the semiconductor substrate 100 (rear surface side), arear-surface-irradiation photoelectric conversion device can beobtained.

FIG. 2 illustrates an operation in eight rows in a case where the cellarray 110 includes eight rows of the photoelectric conversion cells 111.In the example illustrated in FIG. 2, progressive scanning is performedon a first row R1 to an eighth row R8. Alternatively, interlace scanningmay be performed.

A drive period Tdr for one photoelectric conversion cell 111 includes areset period Trs in which a reset operation is performed, anaccumulation period Tac in which an accumulation operation foraccumulating charge based on the signal light 82 is performed, and aread period Tsr in which a read operation for reading signals based onaccumulated charge is performed. The read period Tsr may also bereferred to as a period in which output from the photoelectricconversion cell to the column wiring line is performed. The drive periodTdr may further include a period in which another desired operation isperformed. In this example, the plurality of photoelectric conversioncells 111 belonging to the same row are simultaneously driven within asingle drive period Tdr. The signals output from the plurality ofphotoelectric conversion cells 111 belonging to the same row of the cellarray 110 are processed by the signal processing part 160 and are outputto the output part 180, as described above with reference to FIG. 1B.

A frame period is a period in which reset operations, accumulationoperations, and read operations are performed in all the rows of thephotoelectric conversion cells 111 constituting the cell array 110. Forexample, the starting point of a first frame period F1 is the time pointat which the reset operation in the first row R1 is started, and the endpoint of the first frame period F1 is the time point at which the readoperation in the photoelectric conversion cells 111 in the eighth row R8is ended. The starting point of a second frame period F2 is the timepoint at which the reset operation in the first row R1 is started forthe first time after the read operation in the first row R1 is ended inthe first frame period F1. The end point of the second frame period F2is the time point at which the read operation in the eighth row R8 isended for the first time after the read operation in the eighth row R8is ended in the first frame period F1.

As illustrated in FIG. 2, the accumulation operations in a plurality ofrows (in this example, three to four rows) are performed in parallel,and thus the accumulation period can be extended and the output ofsignals obtained in the accumulation period can be increased. Even whenthe accumulation operations in a plurality of rows are performed inparallel, signals in the plurality of rows can be separated from oneanother by making the read operation timing different among the rows.

Furthermore, as a result of performing a series of operations so thatpart of the first frame period F1 overlaps part of the second frameperiod F2 as illustrated in FIG. 2, the frame rate can be increased orone frame period can be extended. That is, in FIG. 2, at the time whenthe read operations in the first to fourth rows are ended in the firstframe period F1, the reset operation and the accumulation operation inthe first row are started.

The embodiment is not limited to this example. After all the resetoperation, accumulation operation, and read operation in one row havebeen ended, the reset operation, accumulation operation, and readoperation in the next row may be started. Alternatively, after the readoperation in the last row (eighth row) has been ended, the resetoperation in the first row may be started.

Next, a description will be given of an example structure of eachphotoelectric conversion cell 111. FIG. 3 illustrates an equivalentcircuit of the photoelectric conversion cell 111. In FIG. 3, theelements included in the photoelectric conversion cell 111 as arepetition unit of the matrix are surrounded by a chained line. Notethat, regarding the elements surrounded by a broken line, part of theelements may be located outside the cell array 110 (for example, thedriving part 140).

The photoelectric conversion cell 111 includes a photoelectricconversion portion 301 and a photoelectric conversion portion 302. Thephotoelectric conversion portion 301 generates electrons as signalcharge through photoelectric conversion, whereas the photoelectricconversion portion 302 generates holes as signal charge throughphotoelectric conversion. That is, the positive/negative sign of thesignal charge generated by the photoelectric conversion portion 301 isopposite to that of the signal charge generated by the photoelectricconversion portion 302. However, the photoelectric conversion portion301 generates holes as well as electrons and the photoelectricconversion portion 302 generates electrons as well as holes. Each of thephotoelectric conversion portions 301 and 302 is a PN photodiode or PINphotodiode, and may be a buried photodiode in view of reducing darkcurrent. Using buried photodiodes as the photoelectric conversionportions 301 and 302 is beneficial in terms of reducing dark currentcompared to the case of using photogates as the photoelectric conversionportions 301 and 302 and increasing the S/N ratio that is important toreceive weak signal light. The photodiode serving as the photoelectricconversion portion 301 includes a cathode 201, which is an n-typesemiconductor region where electrons are majority carriers, and an anode211, which is a p-type semiconductor region where electrons are minoritycarriers. The photodiode serving as the photoelectric conversion portion302 includes an anode 202, which is a p-type semiconductor region whereholes are majority carriers, and a cathode 212, which is an n-typesemiconductor region where holes are minority carriers.

The photoelectric conversion cell 111 includes a capacitor portion 307capable of holding electrons as signal charge generated by thephotoelectric conversion portion 301, and a capacitor portion 310capable of holding holes as signal charge generated by the photoelectricconversion portion 302.

The capacitor portion 307 includes a reference node 217 and a collectionnode 207. The collection node 207 collects electrons as signal chargegenerated by the photoelectric conversion portion 301. The capacitorportion 307 is configured so that a potential difference correspondingto the amount of charge held by the capacitor portion 307 appearsbetween the collection node 207 and the reference node 217. That is, thecapacitor portion 307 functions as a charge-to-voltage conversionportion that converts the amount of charge to a voltage. The capacitorportion 310 includes a reference node 200 and a collection node 210. Thecollection node 210 collects holes as signal charge generated by thephotoelectric conversion portion 302. The capacitor portion 310 isconfigured so that a potential difference corresponding to the amount ofcharge held by the capacitor portion 310 appears between the collectionnode 210 and the reference node 200. That is, the capacitor portion 310functions as a charge-to-voltage conversion portion that converts theamount of charge to a voltage.

The capacitor portions 307 and 310 each have a p-n junction diodestructure. The reference node 217 and the collection node 210 are p-typesemiconductor regions, whereas the reference node 200 and the collectionnode 207 are n-type semiconductor regions. The collection nodes 207 and210 that hold signal charge are floating nodes that are electricallyfloating. The semiconductor regions constituting the collection nodes207 and 210 are impurity diffusion regions in a floating state, that is,floating diffusion. The collection node 207, which is an n-typesemiconductor region, may collect electrons as signal charge and holdthe electrons. The collection node 210, which is a p-type semiconductorregion, may collect holes as signal charge and hold the holes. Althoughthe details will be described below, the photoelectric conversion device11 is capable of operating so that signal charge is selectively held byone of the collection nodes 207 and 210.

The photoelectric conversion cell 111 includes a transfer portion 303 inorder to efficiently collect electrons, among the electrons and holesgenerated by the photoelectric conversion portion 301, to the collectionnode 207 of the capacitor portion 307. Also, the photoelectricconversion cell 111 includes a transfer portion 306 in order toefficiently collect holes, among the electrons and holes generated bythe photoelectric conversion portion 302, to the collection node 210 ofthe capacitor portion 310. Thus, the collection nodes 207 and 210 canalso be referred to as nodes to which signal charge is transferred fromthe photoelectric conversion portions 301 and 302, respectively. Sincethe collection nodes 207 and 210 are capable of holding the chargetransferred from the photoelectric conversion portions 301 and 302, thecollection nodes (capacitor portions) can also be referred to as chargeholding portions.

The transfer portions 303 and 306 each have an MIS gate structure.Specifically, the transfer portions 303 and 306 have a multilayerstructure including a semiconductor region (channel region), a gateinsulating film, and a gate electrode. Thus, the transfer portions 303and 306 can also be referred to as transfer gates. When the transferportion 303 is in an ON state (conducting state), inversion forms ann-type channel in the semiconductor region. When the transfer portion306 is in an ON state, inversion forms a p-type channel in thesemiconductor region. In this way, the conductivity types of thetransfer portions 303 and 306 are different from each other.

In this example, the gate electrode of the transfer portion 303 and thegate electrode of the transfer potion 306 are connected in common to atransfer node 218. The transfer node 218 is connected to a transfersignal output portion 428, and a transfer signal TX1 is input from thetransfer signal output portion 428 to the transfer node 218. Thetransfer portions 303 and 306 have different conductivity types and areconfigured to operate complementarily. That is, the transfer portion 306is in an OFF state (non-conducting state) in a period when the transferportion 303 is in an ON state in response to the transfer signal TX1,and the transfer portion 306 is in an ON state in a period when thetransfer portion 303 is in an OFF state in response to the transfersignal TX1.

A threshold may be set so that both the transfer portions 303 and 306are brought into an OFF state when the transfer node 218 is at apredetermined potential. The predetermined potential may be a potentialbetween the potential at which the transfer portion 303 is in an ONstate and the transfer portion 306 is in an OFF state and the potentialat which the transfer portion 303 is in an OFF state and the transferportion 306 is in an ON state. Such a predetermined potential isdetermined in accordance with the potential in the semiconductor regionin the MIS gate structure and a threshold of the MIS gate structure. Adifference between a potential level High at which the transfer portion303 is in an ON state and a potential level Mid at which the transferportion 303 is in an OFF state is, for example, 1 to 5 V. A differencebetween a potential level Low at which the transfer portion 306 is in anON state and the potential level Mid at which the transfer portion 303is in an OFF state is, for example, 1 to 5 V. The potential level Highmay be set to a potential (positive potential) higher than a groundpotential GND (0 V), and the potential level Low may be set to apotential (negative potential) lower than the ground potential GND. Forexample, the potential level Mid may be set to the ground potential GND.Both the potential levels High and Low may be set to positive potentialsor both the potential levels High and Low may be set to negativepotentials, so as to reduce the circuit scale.

Alternatively, the transfer portions 303 and 306 may be connected todifferent transfer nodes and the ON/OFF states of the transfer portions303 and 306 may be controlled by using transfer signals independent ofeach other. However, it may be better to connect the transfer portions303 and 306 to the same transfer node 218 and input the same transfersignal TX1 to the gate electrodes of the transfer portions 303 and 306.Accordingly, the accuracy of timing control of ON/OFF states of thetransfer portions 303 and 306 can be enhanced. Furthermore, since thetransfer portions 303 and 306 can be driven by the same driving circuitand wiring line, the configuration of the photoelectric conversiondevice 11 can be simplified.

In the above-described manner, the collection node 207 is connected tothe cathode 201 via the transfer portion 303. Also, the collection node210 is connected to the anode 202 via the transfer portion 306.

The collection node 207 may be connected to the cathode 201 without viaan active element such as the transfer portion 303. Also, the collectionnode 210 may be connected to the anode 202 without via an active elementsuch as the transfer portion 306. For example, by maintaining anappropriate relationship between the potential at the photoelectricconversion portion 301 and that at the capacitor portion 307, theelectrons generated by the photoelectric conversion portion 301 can becollected to the collection node 207 even if the transfer portion 303 isomitted. Also, by maintaining an appropriate relationship between thepotential at the photoelectric conversion portion 302 and that at thecapacitor portion 310, the holes generated by the photoelectricconversion portion 302 can be collected to the collection node 210 evenif the transfer portion 306 is omitted. Furthermore, the photoelectricconversion portion 301 may be configured to also function as thecapacitor portion 307 having a capacitance corresponding to the junctioncapacitance thereof, and the photoelectric conversion portion 302 may beconfigured to also function as the capacitor portion 310 having acapacitance corresponding to the junction capacitance thereof. Forexample, a high concentration region where the n-type impurityconcentration is higher than in the other region may be provided in partof the n-type semiconductor region of the photodiode, and the highconcentration region may be used as a collection node. As an alternativeof switching between transfer and non-transfer of charge from thephotoelectric conversion portions 301 and 302 by the transfer portions303 and 306, switching between discharge and non-discharge of chargefrom the photoelectric conversion portions 301 and 302 from dischargeportions connected to the photoelectric conversion portions 301 and 302may be used. However, switching between transfer and non-transfer ofcharge using the transfer portions 303 and 306 enables accurate controlof charge compared to the case of not using the transfer portions 303and 306.

A reference potential supply portion 411 is connected to the anode 211of the photoelectric conversion portion 301 and the reference node 217of the capacitor portion 307. A reference potential VF1 is supplied incommon from the reference potential supply portion 411 to the anode 211of the photoelectric conversion portion 301 and the reference node 217of the capacitor portion 307. A reference potential supply portion 412is connected to the cathode 212 of the photoelectric conversion portion302 and the reference node 200 of the capacitor portion 310. A referencepotential VF2 is supplied in common from the reference potential supplyportion 412 to the cathode 212 of the photoelectric conversion portion302 and the reference node 200 of the capacitor portion 310.

As described above, the photoelectric conversion portion 301 alsogenerates holes, but the holes are discharged to the anode 211 side. Thephotoelectric conversion portion 302 also generates electrons, but theelectrons are discharged to the cathode 212 side.

The collection node 207 of the capacitor portion 307 and the collectionnode 210 of the capacitor portion 310 are connected in common to adetection node 220. A potential corresponding to the amount of electronstransferred from the photoelectric conversion portion 301 to thecapacitor portion 307 and the capacitance of the capacitor portion 307appears at the collection node 207 and the detection node 220. Also, apotential corresponding to the amount of holes transferred from thephotoelectric conversion portion 302 to the capacitor portion 310 andthe capacitance of the capacitor portion 310 appears at the collectionnode 210 and the detection node 220. As a result, a potential that isthe combination of the potential that may appear at the detection node220 due to the electrons collected by the collection node 207 and thepotential that may appear at the detection node 220 due to the holescollected by the collection node 210 appears at the detection node 220.

The collection nodes 207 and 210 are electrically connected to eachother. The electrical connection between the collection nodes 207 and210 is established by a conductor (electrical conductor). Typically, thecollection nodes 207 and 210 are directly connected to each other via aconductor. The conductor has a conductivity of 10⁴ S/m or more (aresistivity of 10⁻⁴ Ω·m or less). An insulator has a conductivity of10⁻⁷ S/m or less (a resistivity of 10⁻⁷ Ω·m or more). A semiconductorhas a conductivity between 10⁻⁷ S/m and 10⁴ S/m (a resistivity between10⁻⁴ Ω·m and 10⁷ Ω·m). Examples of the conductor include metal, metalcompound, graphite, and polysilicon. Silicon with a high impurityconcentration (10¹⁹/cm³ or more) is also considered to have conductivebehavior. Since the collection nodes 207 and 210 are connected to eachother via a conductor, charge is smoothly transmitted and receivedbetween the collection nodes 207 and 210. This shortens the time untilthe potentials at the collection nodes 207 and 210 become static.

It is considered that the following phenomenon will occurtransitionally. First, a difference occurs between the amount ofelectrons collected by the collection node 207 and the amount of holescollected by the collection node 210. In accordance with thisdifference, a potential difference occurs between the collection nodes207 and 210. Electrons move between the collection nodes 207 and 210 viathe conductor so as to reduce the potential difference. Then, theelectrons and holes are recombined (pair annihilation) at the collectionnode 210. Accordingly, a potential corresponding to the amount of chargeas a difference between the amount of electrons collected by thecollection node 207 and the amount of holes collected by the collectionnode 210 appears at the detection node 220.

In this example, since the collection nodes 207 and 210 are directlyconnected to each other via the conductor, the potentials at thecollection nodes 207 and 210 and the detection node 220 can be regardedas the same. Also, for example, a switch may be provided between thecollection node 207 and the detection node 220 and/or between thecollection node 210 and the detection node 220. Accordingly, driving canbe temporarily performed so that at least two of the collection nodes207 and 210 and the detection node 220 have different potentials.

The potential at the detection node 220 is represented by VN, thepotential at the collection node 207 is represented by VN1, and thepotential at the collection node 210 is represented by VN2. Here, theindividual potentials VN, VN1, and VN2 are variable potentials. Asdescribed above, in the embodiment, the collection nodes 207 and 210 areconnected in common to the detection node 220 and thus VN≈VN1≈VN2 issatisfied. In view of the ease of collecting the electrons of thecathode 201 of the photoelectric conversion portion 301 by thecollection node 207, it may be better to satisfy VF1<VN1. Also, in viewof the ease of collecting the holes of the anode 202 of thephotoelectric conversion portion 302 by the collection node 210, it maybe better to satisfy VN2<VF2. Regarding VF1<VN1 and VN2<VF2, VF1<VF2 issatisfied because VN1=VN2. Such a relationship in which the referencepotential VF2 is higher than the reference potential VF1 (VF1<VF2) ismore beneficial to increase the ranging accuracy than a relationship inwhich the reference potential VF2 is equal to or lower than thereference potential VF1 (VF1≧VF2). In this way, the efficiency ofcollecting charge increases, and also high-speed operation and highlyaccurate signal acquisition can be realized. From a practical point ofview, in one embodiment, the potential difference between the referencepotentials VF1 and VF2 may be 0.10 V or more. For this purpose, thereference potential supply portions 411 and 412 are separately providedin this example. The potential difference between the referencepotentials VF1 and VF2 is typically 1 V or more and 5 V or less. Thereference potential VF1 may be set to be lower than the ground potentialGND of 0 V (VF1<GND) and the reference potential VF2 may be set to behigher than the ground potential GND of 0 V (GND<VF2). That is, thereference potential VF1 may be a negative potential and the referencepotential VF2 may be a positive potential.

The detection node 220 is connected to a signal generation portion 315.In this example, the signal generation portion 315 is a MOS transistor(amplification transistor) including a gate, source, and drain. Thedetection node 220 is connected to the gate of the signal generationportion 315 (amplification transistor).

The drain of the signal generation portion 315 is connected to a powersupply portion 432, and a power supply potential VDD is supplied theretofrom the power supply portion 432. The source of the signal generationportion 315 is connected to a constant current source 430 via a MOStransistor (selection transistor) 316, and the signal generation portion315 constitutes a source follower circuit together with the constantcurrent source 430. At the time of a read operation, a selection signalSL is output from a selection signal supply portion 426 connected to thegate of the selection transistor 316 so that the selection transistor316 is brought into an ON state. Accordingly, the signal generationportion 315 generates a pixel signal corresponding to the potential atthe detection node 220 and outputs the pixel signal to an output line431, which is included in the column wiring lines 130 illustrated inFIG. 1B.

In this example, an electric low-pass filter 433 is provided between thedetection node 220 and the signal generation portion 315. With theelectric low-pass filter 433 being provided, an output from the signalgeneration portion 315 can be stabilized and the ranging accuracy can beenhanced even if the potential at the detection node 220 fluctuates. Theelectric low-pass filter 433 may be formed of a resistor connected inseries to the gate of the amplification transistor and a capacitorconnected in parallel to the gate, but the configuration is not limitedthereto. Alternatively, the electric low-pass filter 433 may be omitted.

A reset potential supply portion 413 is connected in common to thecollection nodes 207 and 210 via a MOS transistor (reset transistor)313. The reset potential supply portion 413 outputs a reset potentialVS1. A reset signal RS1 output from a reset signal output portion 423 tothe gate of the reset transistor 313 causes the reset transistor 313 tobe in an ON state. Accordingly, a potential VS11 corresponding to thereset potential VS1 is supplied from the reset potential supply portion413 to the collection node 207. That is, the potential VN1 at thecollection node 207 becomes equal to the potential VS11 (VN1=VS11).Also, a potential VS12 corresponding to the reset potential VS1 issupplied from the reset potential supply portion 413 to the collectionnode 210. That is, the potential VN2 at the collection node 210 becomesequal to the potential VS12 (VN2=VS12).

At the time of a reset operation, the potential VS11 is supplied to thecollection node 207 of the capacitor portion 307, and thereby theelectrons held by the capacitor portion 307 are discharged to the resetpotential supply portion 413. The potential VS12 is supplied to thecollection node 210 of the capacitor portion 310, and thereby the holesheld by the capacitor portion 310 are discharged to the reset potentialsupply portion 413.

To enhance the ranging accuracy, it is beneficial that the potentialdifference between the potential VS11 and the potential VS12 be lessthan 0.10 V, compared to a case where the potential differencetherebetween is 0.10 V or more. When the potential difference betweenthe potentials VS11 and VS12 is less than 0.10 V regarding thecollection nodes 207 and 210 connected in common to the detection node220, an operation in the accumulation period Tac after the reset periodTrs can be stabilized. To make the potential difference between thepotentials VS11 and VS12 less than 0.10 V, the collection nodes 207 and210 may be connected to each other via a conductor having a highconductivity. Also, to make the potential difference between thepotentials VS11 and VS12 less than 0.10 V, a resistor that causes thedifference between the potentials VS11 and VS12 to be 0.10 V or more maynot be located between the collection nodes 207 and 210. Note that aslight potential difference of less than 0.10 V that may be caused by aninevitably generated resistance or manufacturing error is allowable.

In this example, the potential VS11 is applied to the collection node207 and at the same time the potential VS12 is applied to the collectionnode 210. A switch may be provided between the reset signal outputportion 423 and the collection node 207 and between the reset signaloutput portion 423 and the collection node 210. In this case, the timingto apply the potential VS11 to the collection node 207 may be differentfrom the timing to apply the potential VS12 to the collection node 210.

The potential VS11 may be higher than the reference potential VF1(VF1<VS11). In this case, the efficiency of collecting electrons by thecollection node 207 after the reset period Trs can be enhanced. Also,the potential VS12 may be lower than the reference potential VF2(VS12<VF2). In this case, the efficiency of collecting holes by thecollection node 210 after the reset period Trs can be enhanced. Asdescribed above, when VS11=VS12=VS1 is satisfied, the reset potentialVS1 may be a potential between the reference potential VF1 and thereference potential VF2 (VF1<VS1<VF2) in order to satisfy both VF1<VS11and VS12<VF2.

The potential VS11 can be selected from the range of −5 to +5 V. In oneembodiment the potential VS11 is to be selected from the range of −2 to+2 V, for example. Also, the potential VS12 can be selected from therange of −5 to +5 V, and in one embodiment, the potential VS12 is to beselected from the range of −2 to +2 V, for example. The differencebetween the potential VS11 and the potential VS12 is to be 0. Thecircuit may be designed so as to satisfy VF1<VS11 and VS12<VF2 withinthe above-described ranges of the reference potentials VF1 and VF2 andwithin the above-described ranges of the potentials VS11 and VS12.

In the example illustrated in FIG. 3, a transfer portion 304 and acapacitor portion 308 are connected to the photoelectric conversionportion 301 in a manner similar to the transfer portion 303 and thecapacitor portion 307. That is, a set of the transfer portion 303 andthe capacitor portion 307 and a set of the transfer portion 304 and thecapacitor portion 308 are connected in parallel to the photoelectricconversion portion 301. Likewise, a transfer portion 305 and a capacitorportion 309 are connected to the photoelectric conversion portion 302 ina manner similar to the transfer portion 306 and the capacitor portion310. That is, a set of the transfer portion 306 and the capacitorportion 310 and a set of the transfer portion 305 and the capacitorportion 309 are connected in parallel to the photoelectric conversionportion 302. The transfer portion 304 and the capacitor portion 308 mayhave a configuration similar to the transfer portion 303 and thecapacitor portion 307. The transfer potion 305 and the capacitor portion309 may have a configuration similar to the transfer portion 306 and thecapacitor portion 310.

In this example, the gate electrodes that have an MIS gate structure andthat are respectively included in the transfer portions 304 and 305 areconnected in common to a transfer node 219. The transfer node 219 isconnected to a transfer signal output portion 429. A transfer signal TX2is input from the transfer signal output portion 429 to the transfernode 219. The transfer portions 304 and 305 have different conductivitytypes and are provided complementarily. Thus, the transfer portion 305is in an OFF state (non-conducting state) in a period when the transferportion 304 is in an ON state (conducting state) in response to thetransfer signal TX2, and the transfer portion 305 is in an ON state in aperiod when the transfer portion 304 is in an OFF state in response tothe transfer signal TX2. A threshold may be set so that both thetransfer portions 304 and 305 are brought into an OFF state when thetransfer node 219 is at a predetermined potential. Such a predeterminedpotential is determined in accordance with the potential in thesemiconductor region in the MIS gate structure and a threshold of theMIS gate structure. The difference between the potential level High thatcauses the transfer portion 304 to be in an ON state and the potentiallevel Mid that causes the transfer portion 304 to be in an OFF state is,for example, 1 to 5 V. The difference between the potential level Lowthat causes the transfer portion 305 to be in an ON state and thepotential level Mid that causes the transfer portion 305 to be in an OFFstate is, for example, 1 to 5 V. The potential level High may be set toa potential (positive potential) higher than the ground potential GND (0V), and the potential level Low may be set to a potential (negativepotential) lower than the ground potential GND. For example, thepotential level Mid can be set to the ground potential GND. Both thepotential levels High and Low can be set to a positive potential, orboth the potential levels High and Low can be set to a negativepotential, so as to reduce the circuit scale. The transfer portions 304and 305 may be connected to separate transfer nodes, and the ON/OFFstate of the transfer portions 304 and 305 may be controlled by usingtransfer signals independent of each other. The transfer portions 303and 304 connected to the photoelectric conversion portion 301 may beoperated so that the ON and OFF states are reversed with respect to eachother, that is, complementarily. Specifically, while the transferportion 303 is in an ON state in response to the transfer signal TX1,the transfer portion 304 is in an OFF state in response to the transfersignal TX2. While the transfer portion 303 is in an OFF state inresponse to the transfer signal TX1, the transfer portion 304 is in anON state in response to the transfer signal TX2. Also, the transferportions 305 and 306 connected to the photoelectric conversion portion302 may be operated so that the ON and OFF states are reversed withrespect to each other, that is, complementarily. Specifically, while thetransfer portion 306 is in an ON state in response to the transfersignal TX1, the transfer portion 305 is in an OFF state in response tothe transfer signal TX2. While the transfer portion 306 is in an OFFstate in response to the transfer signal TX1, the transfer portion 305is in an ON state in response to the transfer signal TX2. Accordingly,signal charge from a single photoelectric conversion portion can betransferred alternately by two transfer portions connected to the singlephotoelectric conversion portion.

The capacitor portion 308 causes the electrons transferred from thephotoelectric conversion portion 301 via the transfer portion 304 to becollected to a collection node 208. The capacitor portion 309 causes theholes transferred from the photoelectric conversion portion 302 via thetransfer portion 305 to be collected to a collection node 209. Thecapacitor portions 308 and 309 each have a p-n junction diode structure.The collection node 208 of the capacitor portion 308 is an n-typesemiconductor region, and the collection node 209 of the capacitorportion 309 is a p-type semiconductor region. A reference node 228 ofthe capacitor portion 308 is a p-type semiconductor region, and areference node 229 of the capacitor portion 309 is an n-typesemiconductor region. The reference node 228 is connected to thereference potential supply portion 411 and is supplied with thereference potential VF1. The reference node 229 is connected to thereference potential supply portion 412 and is supplied with thereference potential VF2.

The collection nodes 208 and 209 are connected in common to a resetpotential supply portion 414 via a MOS transistor (reset transistor)314. The reset potential supply portion 414 outputs a reset potentialVS2. A reset signal RS2 output from a reset signal output portion 424causes the reset transistor 314 to be in an ON state. Accordingly, thepotentials at the collection nodes 208 and 209 can be set topredetermined reset potentials.

In the example illustrated in FIG. 3, the charge transferred from thephotoelectric conversion portions to the collection nodes 208 and 209 inthe capacitor portions 308 and 309 is discharged. However, similarly tothe signal generation portion 315, a signal generation portion may beconnected to the capacitor portions 308 and 309 and a signal based onthe charge in the capacitor portions 308 and 309 may be read. In thecase of using such a configuration, the signal generated by the signalgeneration portion on the basis of the charge in the capacitor portions308 and 309 and the signal generated by the signal generation portion onthe basis of the charge in the capacitor portions 307 and 310 can becombined. Accordingly, the intensity of the pixel signal can beenhanced.

Examples of potentials used in the above-described circuit will bedescribed. The ground potential GND is 0 V. In a first example, VS1,VS2=0 V, VF1=−1 V, VF2=+1 V, High=+2 V, Mid=0 V, and Low=−2 V. In asecond example, VS1, VS2=+1 V, VF1=0 V, VF2=+2 V, High=+3 V, Mid=+1 V,and Low=−1 V. The second example is obtained by shifting the individualpotentials in the first example by S (V) and corresponds to the casewhere S=−1. In a third example, VS1, VS2=0 V, VF1=−2 V, VF2=+2 V,High=+4 V, Mid=0 V, and Low=−4 V. The third example is an example inwhich the potentials in the first example are multiplied by T andcorresponds to the case where T=2. The above-described value S may be apositive or negative value, and the above-described value T may be lessthan 1. The second and third examples may be combined, that is, thefirst example may be shifted by S (V) and multiplied by T. The actualpotential values can be appropriately adjusted while maintaining therelationship among values of potentials, the differences in potential,and the relationship among the differences in potential that are graspedfrom the individual potentials in the foregoing three examples.

Next, the operation per drive period Tdr of one photoelectric conversioncell 111 of the ranging apparatus 1 will be described with reference toFIGS. 4A to 4C. In the description given below with reference to FIGS.4A to 4C, the periods p1 to p10 correspond to the period from time t0 tot10.

FIG. 4A illustrates a light emission level Le of the light emittingdevice 21 and light reception levels Lr1 and Lr2 of the photoelectricconversion device 11. The light emitting device 21 is in an OFF state inthe periods p1, p4, p5, p7, and p9 when the light emission level Lecorresponds to an amount of light Loff. The light emitting device 21 isin an ON state in the periods p2, p3, p6, and p8 when the light emissionlevel Le corresponds to an amount of light Lon. In this way, the lightemitting device 21 repeats blinking in one cycle that corresponds to aperiod Tcy from time t1 to time t5. Here, it is assumed that blinking isrepeated three times for simplifying the description. Actually, however,blinking is repeated 100 to 10000 times within the accumulation periodTac every time ranging is performed, and thereby sufficient accuracy canbe ensured.

When the speed of light is represented by c (m/s), a delay time fromlight emission to light reception based on a distance d (m) from theranging apparatus 1 to the target 9 is 2×d/c (s). The delay time fromlight emission to light reception may be detected within one cycle Tcy.The speed of light is 3×10⁸ m/s, that is, 0.3 m/ns. Thus, one cycle Tcyis set to, for example, 1 ns to 1000 ns, and in one embodiment, onecycle Tcy is set to 10 ns to 100 ns. For example, the delay from lightemission to light reception corresponding to a distance difference of0.3 m is 2 ns. Thus, if one cycle Tcy is 10 ns, a distance difference of0.3 m can be detected by detecting a physical amount corresponding tothe delay time within 10 ns. In accordance with the cycle Tcy and thenumber of times blinking is repeated, one ranging operation is carriedout in a short time of 1 μs to 10 ms. Thus, about 10 to 1000 rows of thecell array 110, that is, about 1 to 1000 frames, can be read in onesecond. For example, if the drive period Tdr for one row is 1 μs, 1000frames in 1000 rows can be read in one second. If the drive period Tdrfor one row is 10 ms, 1 frame in 100 rows can be read in one second.

The amount of light received by the photoelectric conversion device 11in response to light emission by the light emitting device 21 isrepresented by Lra and Lrb. The waveform represented by the lightreception level Lr1 indicates that light reception is started at timet2, which is the time when a period Tda has elapsed since time t1 whenlight emission is started, and that light reception is finished at timet4, which is the time when a period Tda has elapsed since time t3 whenlight emission is finished, in accordance with the distance from theranging apparatus 1 to the target. The waveform represented by the lightreception level Lr2 indicates that light reception is started at timet2′, which is the time when a period Tdb has elapsed since time t1 whenlight emission is started, and that light reception is finished at timet4′, which is the time when a period Tdb has elapsed since time t3 whenlight emission is finished, in accordance with the distance from theranging apparatus 1 to the target. In this example, Tda<Tdb and thus itcan be understood that the target that has reflected the signal lightrepresented by the light reception level Lr1 is closer to the rangingapparatus 1 than the target that has reflected the signal lightrepresented by the light reception level Lr2. Furthermore, in thisexample, Lrb<Lra and thus it can be understood that the signal lightrepresented by the light reception level Lr1 is likely to have a higherreflectance than the signal light represented by the light receptionlevel Lr2.

In the period when the photoelectric conversion device 11 receives lightemitted by the light emitting device 21, the amounts of light Lra andLrb received by the photoelectric conversion device 11 include not onlythe signal light 82 but also the ambient light 83 illustrated in FIG.1A. The amount of received ambient light is represented by Lam. Amongthe amounts of light Lra and Lrb, the amount of light obtained bysubtracting Lam therefrom corresponds to signal light having actualdistance information.

FIG. 4B illustrates a temporal change in the reset signals RS1 and RS2(broken line), the selection signal SL (solid line), the transfer signalTX1 (one-dot chained line), and the transfer signal TX2 (two-dot chainedline). The potential level High is higher than the potential level Low,and the potential level Mid is between the potential level High and thepotential level Low. The potential level High, the potential level Mid,and the potential level Low may each include potentials in a certainrange. For example, the potential level Mid is a potential in a certainrange including the ground potential (0 V). In FIG. 4B, the potential atthe position where the horizontal axis representing time is locatedcorresponds to the potential level Mid. Regarding FIG. 4B, a descriptionwill be given under the assumption that, for convenience, transistorsoperate similarly to the case where the potential level is High, at atransitional potential between the potential level Mid and the potentiallevel High (at a rising or falling potential). Also, a description willbe given under the assumption that the transistors operate similarly tothe case where the potential level is Low, at a transitional potentialbetween the potential level Mid and the potential level Low (at a risingor falling potential). The potential levels that cause the individualtransistors to be turned ON and OFF are not necessarily the same and maybe different from one another.

The reset signals RS1 and RS2 are at the potential level High in thesame period, but the periods when the reset signals RS1 and RS2 are atthe potential level High may be different from each other. The transfersignals TX1 and TX2 are typically rectangular waves or sine waves withthe same cycle in which positive and negative signs are inverted. Thecycles of the transfer signals TX1 and TX2 are identical to the cycleIcy in which the light emitting device 21 emits light. However, thecycles of the transfer signals may be slightly different from the lightemission cycle if a decrease in the ranging accuracy is accepted.

In the period p1 when the reset signals RS1 and RS2 are at a potentialhigher than the potential level Mid (typically at the potential levelHigh), the reset transistors 313 and 314 are in an ON state. From timet1 to time t10, which is a period when the reset signals RS1 and RS2 areat the potential level Mid, the reset transistors 313 and 314 are in anOFF state. In FIG. 4A, the illustration is given under the assumptionthat the reset signals RS1 and RS2 are the same. Alternatively, thereset signals RS1 and RS2 may be different from each other in a periodthat is not illustrated.

In the periods p2, p3, p6, and p8 when the transfer signal TX1 is at apotential higher than the potential level Mid (typically at thepotential level High), the transfer portion 303 is in an ON statewhereas the transfer portion 306 is in an OFF state. In the periods p4,p5, p7, and p9 when the transfer signal TX1 is at a potential lower thanthe potential level Mid (typically at the potential level Low), thetransfer portion 303 is in an OFF state whereas the transfer portion 306is in an ON state. The period from when the reset transistors 313 and314 are changed from an ON state to an OFF state to when one of thetransfer portions 303 and 306 is changed to an ON state may be as shortas possible.

In the periods p2, p3, p6, and p8 when the transfer signal TX2 is at apotential lower than the potential level Mid (typically at the potentiallevel Low), the transfer portion 305 is in an ON state whereas thetransfer portion 304 is in an OFF state. In the periods p4, p5, p7, andp9 when the transfer signal TX2 is at a potential higher than thepotential level Mid (typically at the potential level High), thetransfer portion 305 is in an OFF state whereas the transfer portion 304is in an ON state. The period from when the reset transistors 313 and314 are changed from an ON state to an OFF state to when one of thetransfer portions 304 and 305 is changed to an ON state may be as shortas possible.

In the period (or at the time) when the transfer signal TX1 is at thepotential level Mid, the transfer portions 303 and 306 are in an OFFstate. In the period (or at the time) when the transfer signal TX2 is atthe potential level Mid, the transfer portions 304 and 305 are in an OFFstate. The potential level Mid is determined in accordance with thecharacteristics of the transfer portions 303, 304, 305, and 306, asdescribed above.

FIG. 4C illustrates a change in the potential at the detection node 220.A potential change S1 represents the change in the potential accordingto the light reception level Lr1, and a potential change S2 representsthe change in the potential according to the light reception level Lr2.

In the period p1, the potentials at the collection nodes 207 and 210 andthe detection node 220 are set to potentials corresponding to the resetpotential VS1 (the potentials VS11 and VS12) by the reset potentialsupply portion 413.

In the period p2, the electrons generated by the photoelectricconversion portion 301 in accordance with the amount of light Lam of theambient light 83 are transferred to the capacitor portion 307. Whenelectrons are generated by the photoelectric conversion portion 301, thepotential at the cathode 201 becomes higher than the potential at theanode 211. If the potential at the anode 211 is, for example, VF1=−2 V,the potential at the cathode 201 is about −1 V. The reset potential VS1makes the potential at the collection node 207 higher than the potentialat the anode 211 (VF1<VS1). Thus, when the transfer portion 303 is in anON state, electrons that have been generated quickly move to thecollection node 207 at which the potential is higher than that at thecathode 201. In accordance with the transfer of the electrons, thepotential at the detection node 220 connected to the collection node 207decreases.

In the period p3, the electrons generated by the photoelectricconversion portion 301 in accordance with the amount of light Lraincluding the signal light 82, which is larger than the amount Lam ofthe ambient light 83, are transferred to the capacitor portion 307. Inaccordance with the transfer of the electrons, the potential at thedetection node 220 connected to the collection node 207 decreases with alarger gradient than in the period p2. This is because the amount ofreceived light per unit time increases by the amount of the signal light82.

In the period p4, the holes generated by the photoelectric conversionportion 302 in accordance with the amount of light Lra including thesignal light 82, which is larger than the amount Lam of the ambientlight 83, are transferred to the capacitor portion 310. In accordancewith the transfer of the holes, the potential at the detection node 220connected to the collection node 210 increases.

In the periods p2 and p3, the transfer portion 305 is in an ON state.Thus, the holes generated by the photoelectric conversion portion 302 inthe periods p2 and p3 are transferred to the capacitor portion 309 inthe periods p2 and p3. Thus, among the holes transferred to thecapacitor portion 310 after the transfer portion 306 is turned ON attime t3, for example, in the period p4, the amount of holes generated bythe photoelectric conversion portion 302 in the period p4 is larger thanthe amount of holes generated by the photoelectric conversion portion302 in the periods p2 and p3. Ideally, the holes generated by thephotoelectric conversion portion 302 in the periods p2 and p3 are nottransferred to the capacitor portion 310 in the period p4.

In the period p5, the holes generated by the photoelectric conversionportion 302 in accordance with the amount Lam of the ambient light 83are transferred to the capacitor portion 310. In accordance with thetransfer of the holes, the potential at the detection node 220 connectedto the collection node 210 increases.

The same operation is repeated in the periods p6, p7, p8, and p9. In theperiods p4 and p5, the transfer portion 304 is in an ON state. Thus, theelectrons generated by the photoelectric conversion portion 301 in theperiods p4 and p5 are transferred to the capacitor portion 308 in theperiods p4 and p5. Thus, among the electrons transferred to thecapacitor portion 307 after the transfer portion 303 is turned ON attime t5, for example, in the period p6, the amount of electronsgenerated by the photoelectric conversion portion 301 in the period p6is larger than the amount of electrons generated by the photoelectricconversion portion 301 in the periods p4 and p5. Ideally, the electronsgenerated by the photoelectric conversion portion 301 in the periods p4and p5 are not transferred to the capacitor portion 307 in the periodp6.

With such a cycle Tcy being repeated several times, a signal suitablefor ranging from which the component of the ambient light 83 has beenremoved and in which the component of the signal light 82 is integratedcan be obtained.

Regarding the light reception level Lr1, the delay time Ida is less thana quarter of the cycle Tcy (Ida<Tcy/4). Thus, the potential at thedetection node 220 is effectively dominated by the electrons transferredin the period p3, and the potential at the detection node 220 becomeslower than the reset potential VS1 (the absolute value increases). Ifthe delay time Tdb is a quarter of the cycle Tcy as in the lightreception level Lr2 (Tdb=Tcy/4), the amount of electrons and the amountof holes transferred to the collection nodes 207 and 210 within onecycle Tcy are equal to each other, and thus the potential at thedetection node 220 is equal to the reset potential VS1. If the delaytime Tda>Tcy/4, the potential at the detection node 220 is effectivelydominated by the holes transferred in the period p4, and the potentialat the detection node 220 becomes higher than the reset potential VS1(the absolute value increase).

Here, the ON period and OFF period of the light emitting device 21 inone cycle Icy are equal to each other, but the ON period and OFF periodmay be different from each other. If the ON period and OFF period aredifferent from each other, the signal output from the signal generationportion 315 may be corrected on the basis of the difference between theON period and the OFF period. Furthermore, although the ON period andOFF period of the transfer gate in one cycle Icy are equal to each otherhere, the ON period and OFF period may be different from each other. Ifthe ON period and OFF period are different from each other, the signaloutput from the signal generation portion 315 may be corrected on thebasis of the difference between the ON period and the OFF period.

The potential that appears at the detection node 220 will bequantitatively described. Among the electrons serving as signal charge,a component derived from the ambient light 83 is represented by (−N),and a component derived from the signal light 82 is represented by (−S).Among the holes serving as signal charge, a component derived from theambient light 83 is represented by (+N), and a component derived fromthe signal light 82 is represented by (+S). A coefficient proportionalto the length of the period p2 is represented by a, a coefficientproportional to the length of the period p3 is represented by b, acoefficient proportional to the length of the period p4 is representedby c, and a coefficient proportional to the length of the period p5 isrepresented by d.

First, under the assumption that recombination of electrons and holesdoes not occur at the detection node 220, the amounts of charge at thecollection nodes 207 and 210 are calculated. An increase in the amountof charge at the collection node 207 in the period p2 is expressed bya×(−N), and the amount of charge at the collection node 207 at time t2is expressed by a×(−N). On the other hand, an increase in the amount ofcharge at the collection node 210 in the period p2 is 0, and the amountof charge at the collection node 210 at time t2 is 0. An increase in theamount of charge at the collection node 207 in the period p3 isexpressed by b×(−N−S), and the amount of charge at the collection node207 at time t3 is expressed by a×(−N)+b×(−N−S). On the other hand, anincrease in the amount of charge at the collection node 210 in theperiod p3 is 0, and the amount of charge at the collection node 210 attime t3 is 0. An increase in the amount of charge at the collection node207 in the period p4 is 0, and the amount of charge at the collectionnode 207 at time t4 is expressed by a×(−N)+b×(−N−S). An increase in theamount of charge at the collection node 210 in the period p4 isexpressed by c×(+N+S), and the amount of charge at the collection node210 at time t4 is expressed by c×(+N+S). An increase in the amount ofcharge at the collection node 207 in the period p5 is 0, and the amountof charge at the collection node 207 at time t5 is expressed bya×(−N)+b×(−N−S). On the other hand, an increase in the amount of chargeat the collection node 210 in the period p5 is expressed by d×(+N), andthe amount of charge at the collection node 210 at time t5 is expressedby c×(+N+S)+d×(+N).

An actual amount of charge at the detection node 220 at time t5corresponds to that obtained by subtracting electrons and holes, whichis expressed by the following expression:a×(−N)+b×(−N−S)+c×(+N+S)+d×(+N)=(a+b)×(−N)+(c+d)×(+N)+b×(−S)+c×(+S)=((c+d)−(a+b))×N+(c−b)×S.In the period from time t1 to time t5, if the ambient light 83 isconstant and if the periods when the transfer portions 303 and 306 arecomplementarily in an ON state are the same, (c+d)−(a+b)=0 is satisfied.Thus, it is understood that the potential that appears at the detectionnode 220 at time t5 is obtained as a signal which is (c−b)×S from whichat least part of the component of the ambient light 83 has been removedand which indicates only the component of the signal light 82.

FIGS. 5A to 5D illustrate an example layout of the photoelectricconversion cell 111. FIG. 5A is a schematic plan view of thephotoelectric conversion cell 111. FIG. 5B is a schematiccross-sectional view taken along the line VB-VB in FIG. 5A, FIG. 5C is aschematic cross-sectional view taken along the line VC-VC in FIG. 5A,and FIG. 5D is a schematic cross-sectional view taken along the lineVD-VD in FIG. 5A.

The semiconductor substrate 100 is provided with a p-type semiconductorregion 511 serving as a p-type well and an n-type semiconductor region512 serving as an n-type well. For example, the n-type semiconductorregion 512 is an n-type epitaxial layer, whereas the p-typesemiconductor region 511 is a p-type impurity diffusion region formedthrough ion implantation with a p-type impurity into the n-typeepitaxial layer. A plurality of portions constituting a singlesemiconductor region, that is, each of the semiconductor regions 511 and512, have the same conductivity type and are continuous to one another.Here, the plurality of portions are portions whose positions in at leastany of X, Y, and Z directions are different. The plurality of portionsconstituting each of the semiconductor regions 511 and 512 may havedifferent impurity concentrations. For example, the p-type semiconductorregion 511 may have an impurity concentration that inclines in the depthdirection (Z direction) of the semiconductor substrate 100.

In the photoelectric conversion cell 111, the photoelectric conversionportion 301 and the photoelectric conversion portion 302 are arrangedalong a front surface 1000 of the semiconductor substrate 100. Thedirection in which the photoelectric conversion portions 301 and 302 arearranged is the X direction, the direction parallel to the front surface1000 and vertical to the X direction is the Y direction, and thedirection vertical to the front surface 1000 is the Z direction.

As a structure different from that illustrated in FIGS. 5A to 5D, thephotoelectric conversion portions 301 and 302 may be arranged in the Zdirection. That is, one of the photoelectric conversion portions 301 and302 may be located at a position in the semiconductor substrate 100deeper than the other. For example, the cathode (n-type semiconductorregion) of the photoelectric conversion portion 301 and the anode(p-type semiconductor region) of the photoelectric conversion portion302 are located in the Z direction from the front surface 1000. Also,the anode (p-type semiconductor region) of the photoelectric conversionportion 301 and the cathode (n-type semiconductor region) of thephotoelectric conversion portion 302 are located therebetween so as toachieve p-n junction isolation. With a p-type semiconductor regionserving as a charge movement path that is connected to the anode of thephotoelectric conversion portion 302 being extended toward the frontsurface 1000, signal charge of the photoelectric conversion portion 302located at a deep position can be collected through the charge movementpath. In this case, however, the amount of light subjected tophotoelectric conversion by the photoelectric conversion portion at ashallower position is different from the amount of light subjected tophotoelectric conversion by the photoelectric conversion portion at adeeper position, and accordingly a great difference occurs in the amountof signal charge to be generated. This is because the light is absorbedin the semiconductor substrate 100 and is attenuated. Thus, for thepurpose of decreasing the difference in the amount of received lightbetween the photoelectric conversion portions 301 and 302, thephotoelectric conversion portions 301 and 302 may be arranged along thefront surface 1000 of the semiconductor substrate 100.

In FIGS. 5A to 5D, bold lines represent local wiring lines provided inthe photoelectric conversion cell 111. Circles represent the positionsof contact portions that are used to establish a connection between thesemiconductor substrate 100 and the local wiring lines or global wiringlines (not illustrated) such as the row wiring lines 120 and the columnwiring lines 130 described above with reference to FIG. 1B. At a typicalcontact portion, a contact plug and the semiconductor substrate 100 areconnected to each other. Here, a local wiring line is a wiring line forelectrically connecting elements in the photoelectric conversion cell111 to each other. On the other hand, a global wiring line is a wiringline for connecting the photoelectric conversion cells 111 to each otheror connecting the photoelectric conversion cells 111 to a circuitoutside the cell array 110. The row wiring lines 120 and the columnwiring lines 130 described above with reference to FIG. 1B are typicalglobal wiring lines. A wiring line is a member composed of a conductorfor establishing an electrical connection. At a contact portion forestablishing a connection with a semiconductor region, part of thesemiconductor region connected to a conductor such as a contact plug isan impurity region of high concentration compared to the other part, andthereby favorable electrical connection may be ensured.

As illustrated in FIG. 5B, in the Y direction, an n-type semiconductorregion 507, a transfer gate electrode 503, an n-type semiconductorregion 501, a transfer gate electrode 504, and an n-type semiconductorregion 508 are arranged in this order along the line VB-VB.

As illustrated in FIG. 5C, in the Y direction, a p-type semiconductorregion 510, a transfer gate electrode 505, a p-type semiconductor region502, a transfer gate electrode 506, and a p-type semiconductor region509 are arranged in this order along the line VC-VC.

As illustrated in FIG. 5A, in the X direction, a gate electrode 513 ofthe reset transistor 313, a gate electrode 514 of the reset transistor314, a gate electrode 515 of the amplification transistor, and a gateelectrode 516 of the selection transistor 316 are arranged in thisorder. The gate electrode 515 of the amplification transistorconstituting the signal generation portion 315 serves as an input nodeof the signal generation portion 315 and is connected to the detectionnode 220 directly or via the electric low-pass filter 433.

The n-type semiconductor region 507 is part of the capacitor portion 307and constitutes the collection node 207. In other words, the n-typesemiconductor region 507 is a first floating diffusion. Thesemiconductor region 511 forms a p-n junction in conjunction with thesemiconductor region 507, and the semiconductor region 511 constitutesthe reference node 217 of the capacitor portion 307.

The p-type semiconductor region 510 is part of the capacitor portion 310and constitutes the collection node 210. In other words, the p-typesemiconductor region 510 is a second floating diffusion. Thesemiconductor region 512 forms a p-n junction in conjunction with thesemiconductor region 510, and the semiconductor region 512 constitutesthe reference node 200 of the capacitor portion 310.

The n-type semiconductor region 501 is part of the photoelectricconversion portion 301 and constitutes the cathode 201 of thephotodiode. The semiconductor region 501 forms a p-n junction inconjunction with the semiconductor region 511, and the semiconductorregion 511 constitutes the anode 211 of the photodiode. The impurityconcentration of the n-type semiconductor region 501 may be low enoughto be depleted at a built-in potential. Accordingly, in theelectron-hole pairs generated by the photoelectric conversion portion301, the electrons generated as signal charge are less likely to beaccumulated in the photoelectric conversion portion 301. As a result,the transfer efficiency of electrons from the photoelectric conversionportion 301 to the semiconductor region 507 increases. Also, electronsgenerated from light can be completely transferred to the semiconductorregion 507, and noise caused by low transfer efficiency can be reduced.The holes not used as signal charge in the photoelectric conversionportion 301 are discharged through the p-type semiconductor region 511.A front surface region, which is a p-type semiconductor region, isprovided between the n-type semiconductor region 501 and the frontsurface 1000 of the semiconductor substrate 100, and the n-typesemiconductor region 501 is located apart from the front surface 1000.Accordingly, the photoelectric conversion portion 301 serves as a buriedphotodiode. In FIGS. 5A to 5D, the p-type semiconductor region servingas a front surface region is integrated with the p-type semiconductorregion 511.

The p-type semiconductor region 502 is part of the photoelectricconversion portion 302 and constitutes the anode 202 of the photodiode.The semiconductor region 502 forms a p-n junction in conjunction withthe semiconductor region 512, and the semiconductor region 512constitutes the cathode 212 of the photodiode. The impurityconcentration of the p-type semiconductor region 502 may be low enoughto be depleted at a built-in potential. Accordingly, in theelectron-hole pairs generated by the photoelectric conversion portion302, the holes generated as signal charge are less likely to beaccumulated in the photoelectric conversion portion 302. As a result,the transfer efficiency of holes from the photoelectric conversionportion 302 to the semiconductor region 510 increases. Also, holesgenerated from light can be completely transferred to the semiconductorregion 510, and noise caused by low transfer efficiency can be reduced.The electrons not used as signal charge in the photoelectric conversionportion 302 are discharged through the p-type semiconductor region 511.A front surface region, which is an n-type semiconductor region, isprovided between the p-type semiconductor region 502 and the frontsurface 1000 of the semiconductor substrate 100, and the p-typesemiconductor region 502 is located apart from the front surface 1000.Accordingly, the photoelectric conversion portion 302 serves as a buriedphotodiode. In FIGS. 5A to 5D, the n-type semiconductor region servingas a front surface region is integrated with the n-type semiconductorregion 512.

The n-type semiconductor region 508 forms a p-n junction in conjunctionwith the semiconductor region 511. The semiconductor region 508 is partof the capacitor portion 308 and constitutes the collection node 208.The p-type semiconductor region 509 forms a p-n junction in conjunctionwith the semiconductor region 512. The semiconductor region 509 is partof the capacitor portion 309 and constitutes the collection node 209.The n-type semiconductor region 501 and the p-type semiconductor region502 are arranged in the X direction along the front surface 1000. Then-type semiconductor region 501 and the p-type semiconductor region 502are isolated from each other, but may be in contact with each other. Inthis example, the p-type semiconductor region 511 and the n-typesemiconductor region 512 form a p-n junction between the n-typesemiconductor region 501 and the p-type semiconductor region 502.Accordingly, the semiconductor region 501 and the semiconductor region502 are electrically isolated from each other (p-n junction isolation).

The reference potential VF1 is supplied to the semiconductor region 511from a contact plug 611 that constitutes the reference potential supplyportion 411. Also, the reference potential VF2 is supplied to thesemiconductor region 512 from a contact plug 612 that constitutes thereference potential supply potion 412. The reference potential VF1 islower than the reference potential VF2, and thereby a reverse biasvoltage is applied between the semiconductor regions 511 and 512. Thus,a depletion layer generated between the semiconductor regions 511 and512 causes the semiconductor regions 511 and 512 to be electricallyisolated from each other. Accordingly, the electrons generated by then-type semiconductor region 501 and the holes generated by the p-typesemiconductor region 502 can be electrically isolated from each other.Thus, charge can be collected by a corresponding collection node atappropriate timing and signal charges for ranging can be selectivelyrecombined. Also, the photoelectric conversion portions 301 and 302 areisolated from each other by p-n junction isolation and thereby theinterval between the photoelectric conversion portions 301 and 302 canbe decreased (for example, less than 1 μm). Accordingly, the differencein the amount of received light between the photoelectric conversionportions 301 and 302 can be decreased. Furthermore, the p-n junctionisolation is able to suppress the occurrence of dark current compared toinsulator isolation.

In the cell array 110, the photoelectric conversion cells 111 eachhaving the structure illustrated in FIG. 5A are arranged in a matrix.The n-type semiconductor region 512 is provided among the plurality ofphotoelectric conversion cells 111, serving as a continuous common well.On the other hand, the p-type semiconductor region 511 is provided amongthe plurality of photoelectric conversion cells 111, serving as adiscontinuous isolated well. That is, the p-type semiconductor region511 of a certain photoelectric conversion cell 111 may be electricallyisolated from the p-type semiconductor region 511 of at least one of theadjoining photoelectric conversion cells 111 by isolation such as p-njunction isolation. Contrary to the above-described example, the n-typesemiconductor region 512 may serve as an isolated well and the p-typesemiconductor region 511 may serve as a common well. In this way, withuse of one of the n-type semiconductor region 512 and the p-typesemiconductor region 511 as a common well, the configuration of thephotoelectric conversion cell 111 can be simplified.

In plain view, the transfer gate electrode 503 that includes at least aportion located between the n-type semiconductor region 501 and then-type semiconductor region 507 constitutes the transfer portion 303. Inthis example, the transfer gate electrode 503 is located above part ofthe semiconductor region 501 and part of the semiconductor region 507.In plain view, the transfer gate electrode 504 that includes at least aportion located between the n-type semiconductor region 501 and then-type semiconductor region 508 constitutes the transfer portion 304. Inthis example, the transfer gate electrode 504 is located above part ofthe semiconductor region 501 and part of the semiconductor region 508.

In plain view, the transfer gate electrode 505 that includes at least aportion located between the p-type semiconductor region 502 and thep-type semiconductor region 510 constitutes the transfer portion 306. Inthis example, the transfer gate electrode 505 is located above part ofthe semiconductor region 502 and part of the semiconductor region 510.In plain view, the transfer gate electrode 506 that includes at least aportion located between the p-type semiconductor region 502 and thep-type semiconductor region 509 constitutes the transfer portion 305. Inthis example, the transfer gate electrode 506 is located above part ofthe semiconductor region 502 and part of the semiconductor region 509.

An insulating film 500 is provided between the semiconductor substrate100 and the transfer gate electrodes 503, 504, 505, and 506. Theinsulating film 500 functions as a gate insulating film.

A local wiring line 618 is connected in common to the transfer gateelectrodes 503 and 505 via contact plugs 603 and 605 so that the sametransfer signal TX1 is supplied to the transfer gate electrodes 503 and505. Here, the transfer gate electrodes 503 and 505 are provided asseparate gate electrodes. A gate electrode performs charge/dischargeevery time it is driven and thus a current corresponding to MOScapacitance flows every time switching is performed. In the case ofperforming high-speed driving, the MOS capacitance decreases as the sizeof the gate electrode of the transistor decreases, and accordingly asmall current flows and power is saved. Thus, with the transfer gateelectrodes 503 and 505 being provided separately, the size of the gateelectrodes can be decreased as much as possible.

Alternatively, an integrated gate electrode including a portion servingas the transfer portion 303 and a portion serving as the transferportion 305 may be provided. With this configuration, the number ofwiring lines can be decreased and the wiring capacitance and resistancecan be decreased, and accordingly the accuracy of complementary controlof the transfer portions 303 and 305 can be enhanced. Furthermore, adecreased number of wiring lines enables a higher aperture ratio andhigher sensitivity. The same applies to the transfer gate electrodes 504and 506.

A reset transistor including the gate electrode 513 is connected to thesemiconductor regions 507 and 510 via contact plugs 607 and 610, a localwiring line 620, and a contact plug 613. In this example, the localwiring line 620 constitutes the detection node 220. The gate electrode513 is connected to the reset signal output portion 423 outside the cellarray via a contact plug, a local wiring line, and a global wiring line.The contact plug 613 is connected to a semiconductor region 523, whichcorresponds to one of source/drain regions of the reset transistor. Theother source/drain regions of the reset transistor are connected to thereset potential supply portion 413 outside the cell array via a globalwiring line. Also, a reset transistor including the gate electrode 514is connected to the semiconductor regions 508 and 509 via a local wiringline and a contact plug.

The amplification transistor including the gate electrode 515 isconnected to the semiconductor regions 507 and 510 via the local wiringline 620 and a contact plug 615. The contact plug 615 is connected tothe gate electrode 515 of the amplification transistor. The drain of theamplification transistor is connected to the power supply portion 432via a contact plug and a global wiring line. The source of theamplification transistor is connected to the drain of the selectiontransistor 316 including the gate electrode 516. The source of theselection transistor 316 is connected to a global wiring line (thecolumn wiring lines 130) via a contact plug.

The contact plug 611 is connected to the semiconductor region 511. Thecontact plug 611 is connected to the reference potential supply portion411 outside the cell array 110 via a global wiring line. The contactplug 612 is connected to the semiconductor region 512. The contact plug612 is connected to the reference potential supply portion 412 outsidethe cell array 110 via a global wiring line. In this way, a referencepotential is supplied to the semiconductor regions 511 and 512 viawiring lines, and thereby variations in the reference potential in theindividual photoelectric conversion cells 111 in the cell array 110 canbe decreased. Alternatively, a reference potential may be suppliedwithout locating the contact plugs 611 and 612 in the photoelectricconversion cells 111. In this case, an impurity diffusion layerextending from the inside of the cell array 110 to the outside thereofmay be provided on the semiconductor substrate 100, and a referencepotential may be supplied to the impurity diffusion layer outside thecell array 110 via a wiring line and a contact plug. However, asdescribed above, when the p-type semiconductor region 511 is an isolatedwell, it is difficult to extend the p-type semiconductor region 511 tothe outside of the cell array 110. Thus, regarding at least an isolatedwell, a reference potential may be supplied thereto via a conductorprovided on the semiconductor substrate 100, such as a global wiringline, a local wiring line, and a contact plug. The same applies to thecase where the n-type semiconductor region 512 is an isolated well.

The semiconductor regions 507 and 510 are connected to each other via aconductor. In this example, the conductor that connects thesemiconductor regions 507 and 510 includes the local wiring line 620 andthe contact plugs 607 and 610. The conductor that connects thesemiconductor regions 507 and 510 is made of a material with a higherconductivity than the semiconductor substrate 100, such as a metallicmaterial, a metal compound material, or polysilicon. A metallic materialand a metal compound material are used for wiring lines and contactplugs, and polysilicon is used for gate electrodes. The metal compoundmaterial may be a semiconductor-metal compound material such assilicide. These materials are used alone or in combination to connectthe semiconductor regions 507 and 510. In this way, the semiconductorregions 507 and 510 are connected to each other via a conductor and thusthe semiconductor regions 507 and 510 can be connected to each otherwithout using a p-n junction. Typically, the semiconductor regions 507and 510 can be connected to each other via an ohmic contact. With thesemiconductor regions 507 and 510 being connected to each other via aconductor, a configuration in which the semiconductor regions 507 and510 do not form a p-n junction is obtained. Thus, in the case ofrecombining electrons and holes, the time for alleviating a potentialdifference between the semiconductor regions 507 and 510 can beshortened. As a result, the output of the detection node 220 can bestabilized and highly accurate ranging can be realized.

FIGS. 6A to 6D illustrate example structures for obtaining theelectrical connection between the semiconductor regions 507 and 510.FIGS. 6A to 6D correspond to a cross-section including the transfer gateelectrodes 503 and 505 and the semiconductor regions 507 and 510illustrated in FIG. 5A. FIG. 6A illustrates a structure for obtainingthe electrical connection between the semiconductor regions 507 and 510in FIGS. 5A to 5D. FIGS. 6B to 6D illustrate forms different from theform in FIG. 6A for obtaining the electrical connection between thesemiconductor regions 507 and 510. In FIGS. 6A to 6D, the transfer gateelectrodes 503 and 505 are electrically connected to each other via thelocal wiring line 618. The local wiring line 618 is in contact with thecontact plug 603 on the transfer gate electrode 503 and the contact plug605 on the transfer gate electrode 505. The contact plugs 603 and 605extend through an interlayer insulating film 526, and the local wiringline 618 is located on the interlayer insulating film 526. The localwiring line 618 may be, for example, an aluminum wiring line including aconductive portion mainly containing aluminum and a barrier metalportion including a titanium layer and/or titanium nitride layer.Alternatively, the local wiring line 618 may be a copper wiring lineincluding a conductive portion mainly containing copper and a barriermetal portion including a tantalum layer and/or tantalum nitride layer.The copper wiring line has a single damascene structure or dualdamascene structure. The other local wiring lines are also aluminumwiring lines or copper wiring lines.

In the form illustrated in FIG. 6A, the semiconductor regions 507 and510 are connected to each other via the contact plugs 607 and 610 andthe local wiring line 620 that connects the contact plugs 607 and 610.The contact plug 607 is connected to the semiconductor region 507 viathe interlayer insulating film 526, and the contact plug 610 isconnected to the semiconductor region 510 via the interlayer insulatingfilm 526. The contact plugs 607 and 610 each include a conductiveportion mainly containing tungsten and a barrier metal portion that islocated between the conductive portion and the interlayer insulatingfilm 526 and that includes a titanium layer and/or titanium nitridelayer. The local wiring line 620 is an aluminum wiring line including aconductive portion mainly containing aluminum and a barrier metalportion that is located between the conductive portion and theinterlayer insulating film 526 and that includes a titanium layer and/ortitanium nitride layer. Alternatively, the local wiring line 620 is acopper wiring line including a conductive portion mainly containingcopper and a barrier metal portion that is located between theconductive portion and the interlayer insulating film 526 and thatincludes a tantalum layer and/or tantalum nitride layer.

In the form illustrated in FIG. 6B, the semiconductor regions 507 and510 are connected to each other via a contact plug 623, which is aconductor that is in contact with both the semiconductor regions 507 and510. The contact plug 623 includes a conductive portion mainlycontaining tungsten and a barrier metal portion that is located betweenthe conductive portion and the interlayer insulating film 526 and thatincludes a titanium layer and/or a titanium nitride layer. An insulatingfilm 527, which is separated from the insulating film 500 and theinterlayer insulating film 526, is provided between the contact plug 623and the semiconductor substrate 100. The insulating film 527 insulatesthe contact plug 623 and the p-type semiconductor region 511 from eachother and insulates the contact plug 623 and the n-type semiconductorregion 512 from each other. Accordingly, an electrical connectionbetween the p-type semiconductor region 511 and the n-type semiconductorregion 512 can be suppressed.

In the form illustrated in FIG. 6C, the semiconductor regions 507 and510 are connected to each other via a local wiring line 624, which is aconductor that is in contact with both the semiconductor regions 507 and510. The local wiring line 624 can be formed by patterning a tungstenfilm or silicide film. The local wiring line 624 is located between theinterlayer insulating film 526 and the semiconductor substrate 100. Thelocal wiring line 624 may be formed after the transfer gate electrodes503 and 505 have been formed, and then the interlayer insulating film526 and the contact plugs 603 and 605 may be formed. An insulating film528, which is separated from the insulating film 500 and the interlayerinsulating film 526, is provided between the local wiring line 624 andthe semiconductor substrate 100. The insulating film 528 insulates thelocal wiring line 624 and the p-type semiconductor region 511 from eachother and insulates the local wiring line 624 and the n-typesemiconductor region 512 from each other. Accordingly, an electricalconnection between the p-type semiconductor region 511 and the n-typesemiconductor region 512 can be suppressed.

In the form illustrated in FIG. 6D, the semiconductor regions 507 and510 are connected to each other via a local wiring line 625, which is aconductor that is in contact with both the semiconductor regions 507 and510. The local wiring line 625 can be formed by patterning a polysiliconfilm and can be formed at the same time as the transfer gate electrodes503 and 505. The local wiring line 625 is located between the interlayerinsulating film 526 and the semiconductor substrate 100. The insulatingfilm 500 is located between the local wiring line 625 and thesemiconductor substrate 100 so as to achieve insulation between thelocal wiring line 625 and the p-type semiconductor region 511 andinsulation between the local wiring line 625 and the n-typesemiconductor region 512.

The above-described local wiring lines and global wiring lines can beconstituted by connecting a plurality of wiring layers stacked in thedirection vertical to the front surface 1000 of the semiconductorsubstrate 100 to one another by using via plugs.

Next, with reference to FIG. 7, a description will be given of amodification example of the equivalent circuit of the photoelectricconversion cell 111 described above with reference to FIG. 3.

The collection node 207 of the capacitor portion 307 is connected to thedetection node 220 via a switch transistor 318. When a switch signal SW1output from a switch signal output portion 438 causes the switchtransistor 318 to be in an ON state, a potential corresponding to thepotential at the collection node 207 appears at the detection node 220.The collection node 210 of the capacitor potion 310 is connected to thedetection node 220 via a switch transistor 319. When a switch signal SW2output from a switch signal output portion 439 causes the switchtransistor 319 to be in an ON state, a potential corresponding to thepotential at the collection node 210 appears at the detection node 220.In this way, ON/OFF of the electrical connection with the collectionnodes 207 and 210 can be switched in this modification example. In otherwords, the collection nodes 207 and 210 are electrically connected toeach other via the switch transistors 318 and 319. Alternatively, one ofthe switch transistors 318 and 319 may be omitted.

The reset potential supply portion 413 is connected to the collectionnode 207 of the capacitor portion 307 via the reset transistor 313. Thereset signal RS1 output from the reset signal output portion 423 causesthe reset transistor 313 to be in an ON state. Accordingly, the resetpotential VS1 is supplied from the reset potential supply portion 413 tothe collection node 207 of the capacitor portion 307. A reset potentialsupply portion 417 is connected to the collection node 210 of thecapacitor portion 310 via a reset transistor 317. A reset signal RS3output from a reset signal output portion 427 causes the resettransistor 317 to be in an ON state. Accordingly, a reset potential VS3is supplied from the reset potential supply portion 417 to thecollection node 210 of the capacitor portion 310.

In one embodiment, the potential difference between the reset potentialVS1 and the reset potential VS3 is to be less than 0.10 V and thepotential difference between the reset potential VS1 and the resetpotential VS3 is to be 0 V. However, a slight potential difference ofless than 0.10 V due to inevitable resistance or manufacturing error isallowed. The reset potential VS1 and the reset potential VS3 may be apotential between the reference potential VF1 and the referencepotential VF2. For example, the reset potential VS1 may be higher thanthe reference potential VF1 (VF1<VS1). Also, the reset potential VS3 maybe lower than the reference potential VF2 (VS3<VF2). The reset potentialVS1 is, for example, −1 to +1 V. In one embodiment, the reset potentialVS1 is −0.5 to +0.5 V. The reset potential VS3 is, for example, −1 to +1V, and in one embodiment, is −0.5 to +0.5 V.

With the reset potential VS1 being supplied to the capacitor portion307, the electrons held by the capacitor portion 307 are discharged tothe reset potential supply portion 413. With the reset potential VS3being supplied to the capacitor portion 310, the holes held by thecapacitor portion 310 are discharged to the reset potential supplyportion 417. According to this modification example, one of a signalbased on the charge (electrons) obtained through photoelectricconversion performed by the photoelectric conversion portion 301 and asignal based on the charge (holes) obtained through photoelectricconversion performed by the photoelectric conversion portion 302 can beselectively read from the detection node 220. With such an operationmode, the photoelectric conversion device 11 capable of executing bothimage capturing and ranging can be obtained.

In this modification example, the capacitor portions 308 and 309 may beomitted so as to quickly discharge unnecessary charge by turning ON/OFFthe transfer portions 304 and 305. With this configuration, an apertureratio and the area of the photoelectric conversion portions can beincreased by reducing the number of wiring lines, and the sensitivitycan be increased.

FIG. 8 illustrates an example of the operation of the circuitillustrated in FIG. 7. There are a read period Tnr in which the ambientlight 83 is read and a removal period Tcl in which the component of theambient light 83 is removed between the accumulation period Tac and theread period Tsr illustrated in FIG. 2. In the accumulation period Tacafter the reset period Trs, the switch transistor 318 is in an ON stateand the switch transistor 319 is in an OFF state. In the read periodTnr, the selection transistor 316 is in an ON state while the switchtransistor 318 remains in an ON state and the switch transistor 319remains in an OFF state. Accordingly, a signal at the detection node 220at which a potential corresponding to the potential at the collectionnode 207 appears is read. After the read period Tnr, there is theremoval period Tcl in which at least part of the component of theambient light 83 is removed. In the removal period Tcl, the selectiontransistor 316 is in an OFF state, and the switch transistors 318 and319 illustrated in FIG. 7 are in an ON state. Accordingly, recombinationbetween the electrons and holes cancels out the component of the ambientlight 83. Then the potential from which the component of the ambientlight 83 has been removed appears at the detection node 220. In the readperiod Tsr, the selection transistor 316 is brought into an ON state toread a signal from which the component of the ambient light 83 has beenremoved. As a result of reading the ambient light 83 in this manner, notonly an image including distance information but also an image based onthe ambient light 83 can be obtained.

Application examples of the information processing system SYS will bedescribed with reference to FIG. 1A.

A first application example of the information processing system SYS isan example of applying it to a camera equipped with an image capturingapparatus. The information processing apparatus 2 operates the rangingapparatus 1 upon receipt of a signal indicating an instruction toperform ranging from the control apparatus 3 including an input unitsuch as a focus control unit (for example, a focus button).Subsequently, the ranging apparatus 1 outputs a signal includingdistance information representing the distance to the target 9, which isa subject, to the information processing apparatus 2. The informationprocessing apparatus 2 processes the signal and generates a drive signalfor driving mechanical components such a lens, diaphragm, and shutter soas to set conditions suitable for capturing an image of the target 9.The information processing apparatus 2 then outputs the drive signal tothe driving apparatus 4 such as a motor that drives the lens, diaphragm,and shutter. The driving apparatus 4 drives these mechanical componentsin response to the drive signal. Upon receipt of a signal indicating aninstruction to capture an image from the control apparatus 3, theinformation processing apparatus 2 instructs the image capturingapparatus 5 to capture an image, and accordingly the image capturingapparatus 5 captures an image of the target 9. The informationprocessing apparatus 2 displays the image obtained from the imagecapturing apparatus 5 on the display apparatus 6. The informationprocessing apparatus 2 is capable of displaying the obtained image onthe display apparatus 6 together with distance information. Thecommunication apparatus 7 communicates with a storage apparatus or anetwork and stores the image in the storage apparatus or a storage overthe network.

A second application example of the information processing system SYS isan example of applying it to a video information processing system thatprovides a user with mixed reality. When the information processingapparatus 2 operates the ranging apparatus 1 and the image capturingapparatus 5, the image capturing apparatus 5 captures an image of thetarget 9 as a subject and outputs it as a real image. On the other hand,the ranging apparatus 1 outputs a signal including distance informationrepresenting the distance to the target 9 as a subject. The informationprocessing apparatus 2 processes the signal and generates a compositeimage by combining a virtual image formed by using computer graphics orthe like and the real image obtained through capturing by the imagecapturing apparatus 5 on the basis of the distance information. Theinformation processing apparatus 2 displays the composite image on thedisplay apparatus 6 such as a head mounted display.

A third application example of the information processing system SYS isan example of applying it to transportation equipment that moves underpower (for example, a car or train). Upon receipt of a signal indicatingan instruction to move the transportation equipment or to get ready tomove it from the control apparatus 3 that includes a device forgenerating a signal to start an engine (for example, a start button) andan input unit such as a handle and accelerator, the informationprocessing apparatus 2 operates the ranging apparatus 1. The rangingapparatus 1 outputs a signal including distance information representingthe distance to the target 9 as a subject. The information processingapparatus 2 processes the signal, and displays a warning on the displayapparatus 6 if, for example, the distance to the target 9 becomes short.The information processing apparatus 2 is capable of displayinginformation representing the distance to the target 9 on the displayapparatus 6. Also, the information processing apparatus 2 is capable ofreducing or increasing the speed of the transportation equipment bydriving the driving apparatus 4 such as a brake or engine on the basisof the distance information. Furthermore, the information processingapparatus 2 is capable of adjusting the relative distance totransportation equipment that is running ahead by driving the drivingapparatus 4 such as a brake or engine on the basis of the distanceinformation.

A fourth application example of the information processing system SYS isan example of applying it to a game system. A user instructs a main bodyof a game machine to use a gesture mode by using the control apparatus 3including an input unit such as a controller. In response to theinstruction from the user, the information processing apparatus 2operates the ranging apparatus 1. Accordingly, the ranging apparatus 1detects a movement (gesture) of the user as distance information. On thebasis of the obtained distance information, the information processingapparatus 2 creates video in which a virtual character in the game isoperated in accordance with the movement of the user. The informationprocessing apparatus 2 displays the video on the display apparatus 6connected to the main body of the game machine (information processingapparatus 2).

As described above, the photoelectric conversion device 11 according tothe embodiment includes a first photodiode (photoelectric conversionportion 301) that generates electrons and a second photodiode(photoelectric conversion portion 302) that generates holes.Furthermore, the photoelectric conversion device 11 includes the n-typefirst semiconductor region 507 that collects the electrons generated bythe first photodiode (photoelectric conversion portion 301) and thep-type second semiconductor region 510 that collects the holes generatedby the second photodiode (photoelectric conversion portion 302).Furthermore, the photoelectric conversion device 11 includes the signalgeneration portion 315 to which the first semiconductor region 507 andthe second semiconductor region 510 are connected in common.Furthermore, the photoelectric conversion device 11 includes thereference potential supply portion 411 that supplies the referencepotential VF1 to the anode 211 of the first photodiode (photoelectricconversion portion 301) and the reference potential supply portion 412that supplies the reference potential VF2 to the cathode 212 of thesecond photodiode (photoelectric conversion portion 302). The referencepotential VF2 is higher than the reference potential VF1. Such aphotoelectric conversion device is capable of accurately obtaining asignal that is based on electrons and holes.

As described above, the photoelectric conversion device 11 according tothe embodiment includes the photoelectric conversion portion 301 thatgenerates electrons and the photoelectric conversion portion 302 thatgenerates holes. Also, the photoelectric conversion device 11 includesthe n-type semiconductor region 507 that collects the electronsgenerated by the photoelectric conversion portion 301 and the p-typesemiconductor region 510 that collects the holes generated by thephotoelectric conversion portion 302. Furthermore, the photoelectricconversion device 11 includes the signal generation portion 315 to whichthe semiconductor region 507 and the semiconductor region 510 areconnected in common. The difference between the first potential VS11supplied to the semiconductor region 507 and the second potential VS12supplied to the semiconductor region 510 in the reset period Trs is lessthan 0.10 V. Such a photoelectric conversion device is capable ofaccurately obtaining a signal corresponding to the difference in signalcharge between a plurality of photoelectric conversion portions. Also,the photoelectric conversion device is capable of obtaining, with asimple configuration, a signal corresponding to the difference in signalcharge between a plurality of photoelectric conversion portions.

As described above, the photoelectric conversion device 11 according tothe embodiment includes the photoelectric conversion portion 301 thatgenerates electrons and the photoelectric conversion portion 302 thatgenerates holes. Also, the photoelectric conversion device 11 includesthe n-type semiconductor region 507 that collects the electronsgenerated by the photoelectric conversion portion 301 and the p-typesemiconductor region 510 that collects the holes generated by thephotoelectric conversion portion 302. Furthermore, the photoelectricconversion device 11 includes the signal generation portion 315 to whichthe semiconductor region 507 and the semiconductor region 510 areconnected in common. The semiconductor region 507 and the semiconductorregion 510 are connected to each other via the local wiring line 620,which is a conductor. Such a photoelectric conversion device is capableof obtaining, with a simple configuration, a signal corresponding to thedifference in signal charge between a plurality of photoelectricconversion portions. Also, the photoelectric conversion device iscapable of accurately obtaining a signal corresponding to the differencein signal charge between a plurality of photoelectric conversionportions.

As described above, the photoelectric conversion device 11 according tothe embodiment includes the photoelectric conversion portion 301 thatgenerates electrons and the photoelectric conversion portion 302 thatgenerates holes. Also, the photoelectric conversion device 11 includesthe transfer portion 303 that transfers the electrons generated by thephotoelectric conversion portion 301 to the n-type semiconductor region507 and the transfer portion 306 that transfers the holes generated bythe photoelectric conversion portion 302 to the p-type semiconductorregion 510. Furthermore, the photoelectric conversion device 11 includesthe signal generation portion 315 to which the semiconductor region 507and the semiconductor region 510 are connected in common. The transferportion 303 and the transfer portion 306 are connected to the sametransfer node 218. With the potential level High being supplied to thetransfer node 218, the transfer portion 303 is brought into an ON stateand the transfer portion 306 is brought into an OFF state. With thepotential level Low being supplied to the transfer node 218, thetransfer portion 303 is brought into an OFF state and the transferportion 306 is brought into an ON state. Such a photoelectric conversiondevice is capable of accurately obtaining a signal that is based onelectrons and holes. Furthermore, the signal that is based on electronsand holes can be obtained by using a simple configuration.

As described above, the photoelectric conversion device 11 according tothe embodiment includes a first photodiode (photoelectric conversionportion 301) that generates electrons and a second photodiode(photoelectric conversion portion 302) that generates holes.Furthermore, the photoelectric conversion device 11 includes the n-typefirst semiconductor region 507 that collects the electrons generated bythe first photodiode (photoelectric conversion portion 301) and thep-type second semiconductor region 510 that collects the holes generatedby the second photodiode (photoelectric conversion portion 302).Furthermore, the photoelectric conversion device 11 includes the signalgeneration portion 315 to which the first semiconductor region 507 andthe second semiconductor region 510 are connected in common. The p-typesemiconductor region 511 that constitutes the anode 211 of the firstphotodiode (photoelectric conversion portion 301) and the n-typesemiconductor region 512 that constitutes the cathode 212 of the secondphotodiode (photoelectric conversion portion 302) are electricallyisolated from each other by a p-n junction. Such a photoelectricconversion device is capable of obtaining, with a simple configuration,a signal corresponding to the difference in signal charge between aplurality of photoelectric conversion portions. Also, the photoelectricconversion device is capable of accurately obtaining a signalcorresponding to the difference in signal charge between a plurality ofphotoelectric conversion portions.

The photoelectric conversion device is not limited to theabove-described examples and is applicable to various informationprocessing systems SYS. In the above embodiment, a description has beengiven of examples of a photoelectric conversion device optimized toperform driving for ranging, and a ranging apparatus and image capturingsystem including the device. The photoelectric conversion device mayperform driving for something other than ranging. For example, edgedetection for detecting a contour of an object such as a human face,focal point detection using phase difference detection, or ranging maybe performed by using a signal corresponding to the difference in signalcharge between a plurality of photoelectric conversion portions. Suchoperations can be performed because the difference in the amount ofreceived light between a plurality of photoelectric conversion portionscan be detected on the basis of the magnitude of a signal output fromthe signal generation portion in accordance with the difference insignal charge. In general, a complicated structure such as adifferential circuit may be necessary to obtain a difference in electricsignals by converting signal charge into electric signals by using asignal generation portion such as a source follower circuit. However,the photoelectric conversion device according to the embodiment iscapable of easily obtaining a difference in signal charge between aplurality of photoelectric conversion portions by using recombinationbetween electrons and holes. Furthermore, by converting the differencein signal charge into an electric signal by using a signal generationportion having a simple structure, for example, a source followercircuit, the photoelectric conversion device is capable of obtaining asignal corresponding to the difference in signal charge between theplurality of photoelectric conversion portions. With a switch transistorbeing provided between a collection node and a detection node as in theform illustrated in FIG. 7, a signal corresponding to original signalcharge, not a signal corresponding to the difference between theplurality of photoelectric conversion portions, can be read separatelyfrom the signal corresponding to the difference. Accordingly, an imagecapturing operation can be performed.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Applications No.2015-157636, No. 2015-157637, No. 2015-157638, NO. 2015-157639, and No.2015-157640, filed Aug. 7, 2015, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A photoelectric conversion device comprising: afirst photoelectric conversion portion configured to generate electrons;a second photoelectric conversion portion configured to generate holes;a charge-to-voltage conversion portion including an n-type firstsemiconductor region configured to collect the electrons and a p-typesecond semiconductor region configured to collect the holes, thecharge-to-voltage conversion portion being configured to convert acharge that is based on the electrons and the holes to a voltage; and asignal generation portion configured to generate a signal correspondingto the voltage, the signal generation portion including an amplificationtransistor.
 2. The photoelectric conversion device according to claim 1,wherein a difference between a potential supplied to the firstsemiconductor region and a potential supplied to the secondsemiconductor region in a reset period is less than 0.10 V.
 3. Thephotoelectric conversion device according to claim 1, further comprisinga reset potential supply portion connected to the first semiconductorregion via a reset transistor, the reset potential supply portion beingconfigured to supply a potential to the first semiconductor region. 4.The photoelectric conversion device according to claim 3, wherein thereset potential supply portion is connected to the second semiconductorregion via the reset transistor.
 5. The photoelectric conversion deviceaccording to claim 1, wherein the first semiconductor region and thesecond semiconductor region are connected to each other via a conductor.6. The photoelectric conversion device according to claim 1, wherein thefirst semiconductor region and the second semiconductor region areconnected to each other via a conductor, the photoelectric conversiondevice further comprising a reset potential supply portion configured tosupply a reset potential to the conductor.
 7. The photoelectricconversion device according to claim 5, wherein the conductor has aconductivity of 10⁴ S/m or more.
 8. The photoelectric conversion deviceaccording to claim 1, wherein the first photoelectric conversion portionis a first photodiode, and the second photoelectric conversion portionis a second photodiode.
 9. The photoelectric conversion device accordingto claim 8, further comprising: a first potential supply portionconfigured to supply a first potential to an anode of the firstphotodiode; and a second potential supply portion configured to supply asecond potential to a cathode of the second photodiode, wherein thesecond potential is higher than the first potential.
 10. Thephotoelectric conversion device according to claim 9, wherein the firstpotential is lower than a ground potential and the second potential ishigher than the ground potential.
 11. The photoelectric conversiondevice according to claim 8, wherein a p-type third semiconductor regionthat constitutes an anode of the first photodiode and an n-type fourthsemiconductor region that constitutes a cathode of the second photodiodeare electrically isolated from each other by a p-n junction.
 12. Thephotoelectric conversion device according to claim 11, wherein the thirdsemiconductor region and the fourth semiconductor region form the p-njunction between an n-type fifth semiconductor region that constitutes acathode of the first photodiode and a p-type sixth semiconductor regionthat constitutes an anode of the second photodiode.
 13. Thephotoelectric conversion device according to claim 1, furthercomprising: a first transfer potion configured to transfer the generatedelectrons to the first semiconductor region; and a second transferpotion configured to transfer the generated holes to the secondsemiconductor region.
 14. The photoelectric conversion device accordingto claim 13, wherein the first transfer potion and the second transferportion are connected to a common node, and the first transfer portionis turned on and the second transfer portion is turned off by supplyinga first potential to the node, and the first transfer portion is turnedoff and the second transfer portion is turned on by supplying a secondpotential to the node.
 15. The photoelectric conversion device accordingto claim 13, further comprising: a third transfer portion configured totransfer the generated electrons to an n-type semiconductor regiondifferent from the first semiconductor region; and a fourth transferportion configured to transfer the generated holes to a p-typesemiconductor region different from the second semiconductor region. 16.The photoelectric conversion device according to claim 1, wherein theamplification transistor constitutes a source follower circuit, and thecharge-to-voltage conversion portion is electrically connected to a gateelectrode of the amplification transistor.
 17. The photoelectricconversion device according to claim 1, wherein at least one of thefirst semiconductor region and the second semiconductor region iselectrically connected to the signal generation portion via at least oneof an electric low-pass filter and a transistor.
 18. The photoelectricconversion device according to claim 1, wherein the charge-to-voltageconversion portion converts a charge that is based on a differencebetween the electrons collected by the first semiconductor region andthe holes collected by the second semiconductor region to a voltage. 19.The photoelectric conversion device according to claim 1, wherein thefirst photoelectric conversion portion and the second photoelectricconversion portion are arranged on a semiconductor substrate in adirection along a front surface of the semiconductor substrate.
 20. Thephotoelectric conversion device according to claim 1, wherein the firstphotoelectric conversion portion, the second photoelectric conversionportion, the charge-to-voltage conversion portion, and the signalgeneration portion are included in each of cells that are arranged in amatrix.
 21. A ranging apparatus comprising: a light emitting device; andthe photoelectric conversion device according to claim 1, wherein thephotoelectric conversion device receives light emitted by the lightemitting device.
 22. The ranging apparatus according to claim 21,wherein the light emitting device repeats blinking, and collection ofthe electrons to the first semiconductor region and collection of theholes to the second semiconductor region are alternately performed. 23.An information processing system comprising: a ranging apparatusincluding the photoelectric conversion device according to claim 1; andan information processing apparatus configured to process informationobtained from the ranging apparatus.
 24. The information processingsystem according to claim 23, wherein the information processingapparatus performs at least one of a process for displaying informationprocessed by the information processing apparatus on a display apparatusand a process for driving a driving apparatus on the basis ofinformation processed by the information processing apparatus.